An electron-beam dimension measuring apparatus includes: electron-beam irradiating means for irradiating a surface of a sample with an electron beam; a stage on which the sample is placed; a photoelectron generating electrode disposed so as to face the sample; ultraviolet light irradiating means for emitting ultraviolet light; and control means for causing the ultraviolet light irradiating means to irradiate the sample and the photoelectron generating electrode with the ultraviolet light for a predetermined length of time, to cause the sample and the photoelectron generating electrode to emit photoelectrons, for applying a voltage to the photoelectron generating electrode, the voltage applied to supply energy corresponding to a difference between energy of photoelectrons emitted by the sample and energy of photoelectrons emitted by the photoelectron generating electrode, and thereby for controlling an electric potential of the surface of the sample to set the electric potential at 0 V. The control means measures the dimension of the sample after keeping the electric potential constant on the surface of the sample.