A transmission-type target includes a target layer and a transmissive substrate. The target layer is configured to generate X-rays in response to irradiation of electrons. The transmissive substrate supports the target layer and is configured to allow the X-rays generated in the target layer to pass therethrough. The transmissive substrate includes polycrystalline diamond in which grain boundaries extend in a substrate thickness direction and a substrate plane direction. The grain boundaries define an electrical potential of the target layer.