A heat treatment container (1) is provided with support members (6) for supporting a disc-shaped SiC substrate (2), which is an object, at a time of an etching treatment of the SiC substrate (2). Each of the support members (6) has an inclined surface (6F) for supporting a lower surface end (2E) of the SiC substrate (2), the inclined surface being inclined so as to increasingly approach the centerline of the SiC substrate (2) going downward. More specifically, each of the support members (6) is formed in a conical shape with a diameter that increases going downward, and a conical surface which is the peripheral surface of each supporting member forms the inclined surface (6F). A vertically-middle section of the inclined surface (6F) contacts the lower surface end (2E) of the SiC substrate (2).