PURPOSE: To easily and accurately judge whether an image is a normal image or a reflection image by splitting the light emitting body of capturing light of a target into four parts and lighting only a diagonal position and comparing each received output signal of the four elements with each other.

CONSTITUTION: A luminescent body 21 of a reflection mirror part 2 of a target 1 is divided into four parts. Only diagonal positions (A.C or B.D) are lit either at all time or a time when judging a reflection image and the capturing light is received by a capturing light reception part 5 of four split light reception elements 5a-5d. Then, the output signals of upper-half elements 5a and 5b and lower-half elements 5c and 5d are compared with the output signals of right-half elements 5b and 5c and left-half elements 5a and 5d, thus adjusting the direction of a light range-finding means 13c to a state without any difference. In this state, the polarities of output signals of the elements 5a-5d at the ON and OFF positions in a normal image formation for the lighting of the diagonal position of the luminescent body 21 are compared, thus judging whether the image is a regular image or a reflection image according to whether the comparison polarity is the same as or different from the set comparison polarity.