Provided is a substrate processing apparatus comprising: a process chamber for processing a substrate; a heater for heating an interior of the process chamber; a holder for sustaining the substrate in the process chamber; and a substrate transfer plate for transferring the substrate to the holder; wherein the holder has a retainer for sustaining the substrate at its outer periphery and a main body for sustaining the retainer, a portion of the retainer extending at least from a back region thereof with respect to an inserting direction of the substrate transfer plate to a region adjacent thereto and to be sustained by the main body and lying outer than the substrate upon putting the substrate on the retainer being made thicker than other portions of the retainer.