Inner surface strain of a container is reduced by suppressing a temperature drop of blow air, and heat resistance of the container is increased by enhancing the degree of crystallization. A blow air supply unit for a blow molding machine for molding a hollow bottle container 1 by supplying heated blow air into a preform includes: a high-pressure air source 11 for generating high-pressure blow air; a high-pressure gate valve 12 for opening/closing a blow air channel on the downstream of the high-pressure air source 11; a heat exchanger 13 for heating the blow air on the downstream of the high-pressure gate valve 12; a throttle valve 14 for throttling the flow rate of blow air on the downstream side of the heat exchanger 13; and a switchover valve 15 for switching the blow air on the downstream of the throttle valve 14.