PURPOSE: To measure easily and quickly MTF for ≥2 space frequencies by focusing the image of a slit having a very narrow width with a DMLA (roof mirror lens array) and subjecting the light intensity distribution of this image to Fourier conversion.

CONSTITUTION: When a light source lamp 3 is lit, images Im1 and Im2 of slits SL1 and SL2 are focused onto light receiving regions of solid-state image sensors 6 and 5 orthogonally to each other. When solid-state image sensors 5 and 6 are driven in this state, respective slit images Im1 and Im2 are scanned in directions orthogonal to slit images. Consequently, video signals obtained from solid- state image sensors 5 and 6 are subjected to the Fourier conversion operation to measure MTF of a DMLA10 to be examined. If measurement is repeated while displacing the DMLA10 to be examined toward a prescribed direction in the lengthwise direction, MTF in the lengthwise direction of the DMLA10 is measured.