a substrate processing apparatus includes a processing chamber which processes a substrate ; a substrate supporting body which supports the substrate in the processing chamber ; a heating member which heats the substrate and which is disposed on an opposite side from the substrate with respect to the substrate supporting body ; a substrate temperature detecting device provided at a position opposed to a surface of the substrate ; and a light - shielding member which shields stray light from the heating member and which is disposed around the substrate , wherein the light - shielding member has quartz members and an opaque member sandwiched between the quartz members .