In an electron accelerator, a conductive housing defines a cavity. Photoelectrons are emitted from a photocathode into the cavity when light is applied to the photocathode. Via an opening formed in a wall of the conductive housing, the photoelectrons are output to the outside of the cavity. Coolant is flowed through a flow path formed in the wall of the conductive housing, to suppress a temperature rise of the conductive housing. The wall of the conductive housing is made by a metal additive manufacturing technique in such a way as to produce a flow path that has a gentle trajectory without discontinuities in gradient.