A plasma process apparatus that utilizes plasma so as to perform a predetermined process on a substrate, and includes a process chamber that houses a substrate subjected to the predetermined plasma process; a microwave generator; a dielectric window attached to the process chamber and provided with a concave portion provided at an outer surface of the dielectric window opposite to the process chamber and a through hole penetrating the dielectric window to the process chamber; a microwave transmission line; and a first process gas supplying portion including a gas conduit including a first portion provided at a front end and a second portion having a larger diameter than the first portion, the gas conduit being inserted from outside of the process chamber such that the first portion is inserted in the through hole and the second portion is inserted in the concave portion.