To prevent electric charge up from being accumulated on the plane scanned by an electron beam and further to improve the S/N ratio, an electron beam irradiating apparatus comprising: position information signal outputting section for outputting position information signals, in sequence to designate positions at which an electron beam is irradiated on a plane scanned by the electron beam, so as to designate the irradiation positions at random; and irradiation controller for controlling the electron beam to irradiate the electron beam at the irradiation positions in response to the outputted position information signals. Further, to integrate an photoelectric signal over a sufficient time interval within the period of the pixel clock signal, the electric signal detecting circuit comprises a plurality of sample hold circuits and a selecting circuit for selecting and activating the sample hold circuits in sequence.