According to an aspect of an embodiment of the invention, there is provided an electrostatic chuck including: a ceramic dielectric substrate including a first major surface for mounting a clamped target, a second major surface on opposite side from the first major surface, and a through hole provided from the second major surface to the first major surface; a metallic base plate supporting the ceramic dielectric substrate and including a gas feed channel communicating with the through hole; and an insulator plug including a ceramic porous body provided in the gas feed channel and a ceramic insulating film provided between the ceramic porous body and the gas feed channel and being denser than the ceramic porous body, the ceramic insulating film biting into the ceramic porous body from a surface of the ceramic porous body.