1. A latent-image measuring device that measures an electrostatic latent image formed on a sample, the latent-image measuring device comprising: an emitting unit that emits a charged-particle beam to the sample; a detecting unit that detects a charged-particle signal obtained through emission of the charged-particle beam; an optical system that exposes the sample a plurality of times to light to form the electrostatic latent image on the sample; and a charge-distribution measuring unit that measures charge distribution on the sample to determine a state of the electrostatic latent image by in response to exposure of the sample to light the plurality of times by the optical system.