This is an introduction of the apparatus for describing “the Function of Concentration Maintenance”, which has been reported at the First International Congress on Ergonomics held in Stockholm in August, 1961. Our studies reveal that the new method is highly reliable for the evaluation of fatigue and that it will refer a useful means for testing occupation aptitude.<br>The apparatus for TAF-test consists of three parts: gun-barrel, target and oscillograph. The gun-barrel is mounted on a supporting stand, being almost balanced but movable in all directions. Examinee aims at the target in sitting state through a sighting telescope, which is fixed on the gun-barrel, by using a short gun-handle with his right (or left) hand, while his left (or right) eye is covered with a black shade. The target is illuminated by an inside lamp. The light beams from the target are grasped through the muzzle by a photo-receptor installed in the barrel, and are lead to the oscillograph through an amplifier. Then, the changes of the light intensity to the photo-receptor are recorded by oscillograph. Aiming is kept up for a certain period of time and the state of concentration in keeping-up target-aiming will be described as a continuous curve. When the target center is accurately sighted, the oscillogram goes up to the top and in proportion to the inaccuracy in sighting it goes down to the bottom. Thus, the movement of the gun-barrel in sighting is figured in high fidelity.<br>In the present stage the examinee aims at the target at a distance of two meters with the gun-barrel for one minute continuously and rests for ten seconds, while in sitting he must avoid keeping his body stable by grasping the table with his free (left) hand or by putting his (right) elbow on the the table and or to make aiming easier by touching his face with the gun-burrel. In this manner aiming is repeated until he has aimed for a total of three minutes.<br>When the target center is accurately sighted, the level is designated as O and in proportion to the inaccuracy in sighting the numerical figure increases up to 10. From each of the three curves shown during the three minutes, level (L) and deviation (D) are determined. L indicates the height of the average level of these curves and D indicates the standard deviation from L. In this sense the function of concentration maintenance can be expressed by the numerical number with L and D, and variances in TAF-values due to mental and physiological stresses are analysed statistically.<br>As a routine method the TAF-test is given both before and after work, and pre- and post-work values are compared. Suppose, the work gives a certain degree of stress to the examinee, the post-work value will be lowered in comparison with the pre-work value.