An individual beam detector for multiple beams includes a thin film in which a passage hole smaller than a pitch between beams of multiple beams and larger than the diameter of a beam is formed and through which the multiple beams can penetrate, a support base to support the thin film in which an opening is formed under the region including the passage hole, and the width size of the opening is formed to have a temperature of the periphery of the passage hole higher than an evaporation temperature of impurities adhering to the periphery in the case that the thin film is irradiated with the multiple beams, and a sensor arranged, at the position away from the thin film by a distance based on which a detection target beam having passed the passage hole can be detected by the sensor as a detection value with contrast discernible.