This paper investigates the role and position of the Hayashi clan 林家 within the shogunate's political structure and analyzes how their activities influenced the spread of Confucianism in early modern Japan, with a particular focus on Hayashi Gahō 林鵞峰 and his contributions during the reign of Tokugawa Ietsuna (1651-1680). In early modern Japan, a crucial aspect in understanding how and why Confucianism was accepted lies in examining who the bearers of this acceptance were. While there is a scholarly view that Jusha 儒者 (Japanese Confucians) were outside the ordinary social classes, ' this should not be interpreted literally nor seen as reflecting reality. In practice, individual Jusha belonged to various social classes such as the samurai or townspeople. Examining how Confucianism permeated each social class is essential for understanding how it took root by considering social mobility and interaction among these classes. This paper examines the samurai class, especially focusing on those involved in shogunate politics. Within the shogunate, Hayashi Gahō is said to have played a significant role in the acceptance of Confucian ideals, yet his exact position and the role he played remain unclear. Why was the Hayashi clan, despite being Confucians, serving the shogunate even before Confucianism was widely accepted within the shogunate? The founder of the Hayashi clan, Hayashi Razan 林羅山 (1583-1657), was initially a townsman in Kyoto who aspired to be a Confucian scholar. However, he was later appointed as a retainer and was inducted into the samurai class by Tokugawa Ieyasu. We should examine how and why the newly established government sought to integrate the emerging Confucians into its official structure. Gahō, unlike his father Razan, did not serve in close proximity to the shogun. Razan and his brother Tōshū served as close aides to three consecutive shoguns. Gahō, however, was brought into the shogunate through the support of the Rōjū, rather than the shogun. Razan and his brother had dual roles: both in close service to the shogun and involved in administrative duties in coordination with the Rōjū. However, Gahō inherited only the latter role. Gahō's roles can be summarized in five points: (1) creation and editing of written documents in Japanese and Kanbun 漢文 (classical Chinese language); (2) reading aloud of hatto 法度(laws) and legal complaints, which involved performing ceremonial readings of laws on behalf of the shogun and practical readings of complaints at the Hyōjōsho 評定所 (the court); (3) compilation and preservation of records (Razan had compiled many records from the Kan'ei era (1624-1644) under the shogun's orders, and they were preserved by the Hayashi clan and used as precedents for ceremonies. Gahō also compiled records, but under the orders of the Rōjū); (4) engaging in the verification of old records and establishing historical facts in cases such as disputes related to temples and shrines (Gahō's historical texts, compiled through similar activities, were used by the Rōjū as guides for their political actions); (5) lectures on Confucian texts to the Rōjū and daimyo. Through these activities, Confucianism gradually permeated the core of the shogunate. Gahō's thoughts on these roles are reflected in his article “Ichinōshi den” 一能子伝. He idealized a situation in which the shogun would actively engage in governance, with Gahō serving nearby as a Confucian scholar advisor. However, at the time, Confucian knowledge and literature were not given much emphasis, and the shogun did not personally engage in politics. On the other hand, in the absence of a shogun capable of making judgments that could override those of officials and established precedents, the Rōjū had to rely on precedent to handle political affairs. In this context, Gahō, who was proficient in reading and writing and possessed records of the past, became indispensable. During the Ietsuna shogunate, Gahō was not only a shogunate retainer who was affected