A stretching apparatus includes a heat treatment unit 12 configured to perform a heat treatment to a film 8 to be stretched. The heat treatment unit 12 includes a chamber 31, an air supply unit 32 configured to supply air into the chamber 31, an exhaust unit 33 configured to exhaust air from the chamber 31, a pressure measuring unit 34 configured to measure a pressure inside the chamber 31, and a control unit 35. The exhaust unit 33 has an exhaust port 51 provided in the chamber 31 and an exhaust blower 54 capable of exhausting air through the exhaust port 51. The control unit 35 controls the pressure inside the chamber 31 by adjusting an air volume of the exhaust blower 54 based on the pressure measured by the pressure measuring unit 34.