PURPOSE: To test exactly an optical axis even in case when the maximum luminous intensity area is plural head lights, by performing a mean calculation of a tracking stop position co-ordinate of a tester body provided with a sensor for photodetecting the light of a head light, and a tracking stop position co-ordinate after the subsequent forced movement.

CONSTITUTION: When a tester body 4 is moved to the right from the left, etc. and the photodetecting quantity of light of a head light by photodetecting sensors 5a, 5b becomes equal, a motor 7 stops through a movement tracking device 6 and the body 4 stops. A horizontal co-ordinate position of the body 4 in this case is detected by a position detecting sensor 10 and is stored in a storage device 13. At the same time, the body 4 is moved forcibly by a prescribed quantity through a forced moving device 9 for forming a timer responding to a discriminating circuit 6a of the device 6, and a changeover switch 8, and therefore, automatic tracking is executed in he same way, a stop position co-ordinate of the body 4 is stored in the device 13, and storage contents of the device 13 are subjected to mean value processing by a calculation controlling circuit 12. A co-ordinate position in the vertical direction is same as above, is formed by a halogen lamp, and even in case when the maximum luminous intensity area is plural head lights, an optical axis can be tested exactly.