To provide a method and a device for measuring an electrostatic latent image, capable of measuring a highly precise electrostatic latent image by optimizing a measurement image surface to prevent variations in beam diameter.

A device for measuring an electrostatic latent image, which measures the electrostatic latent image on a photoreceptor surface, comprises: an electron gun 11 for electrifying a photoreceptor; an exposure optical system 22 for irradiating the photoreceptor with luminous flux; an acousto-optic deflection element 103 for diffracting the luminous flux in one direction; correction means for correcting field curvature; a polygon mirror 105 for deflecting the diffracted luminous flux in a direction perpendicular to a diffracting direction; the exposure optical system 22 for scanning and exposing the photoreceptor surface by the luminous flux; and a detector 24 for irradiating the exposed photoreceptor with a charged particle beam to detect secondary electrons emitted from the photoreceptor.