An electrostatic chuck having a good soaking feature and allowing a wafer to reach a saturation temperature quickly is provided. The chuck, which has a platy body with a pair of main surfaces, one main surface being used as a mounting surface for mounting a wafer, and an attracting electrode on the other main surface or inside the body, has at least one gas introducing through hole formed so as to pass through the body, a gas flow path formed in the mounting surface by a plurality of mutually separated protrusions and formed so as to communicate with the through hole, and an annular wall portion formed on the outer periphery of the body, characterized in that the planar shape of each of the above protrusions consists of four sides and arc-shaped portions connecting the four sides, and the above protrusions are uniformly arranged on the mounting surface.