To provide a sterilizer preventing ultraviolet ray absorption in a body of a case body and emitting ultraviolet rays to a portion to be sterilized without involving positioning with high accuracy.A sterilizer 1a has a case body 2 containing a member having an ultraviolet-ray transmission property and a flow passage formed thereinside and an ultraviolet-ray irradiation portion 3 irradiating a predetermined portion of a member configuring the case body 2 with ultraviolet rays, in which ultraviolet rays emitted from the ultraviolet-ray irradiation portion 3 travel in a body of the case body 2 to be radiated at least from an end surface on an output end side of the case body 2.
