A manufacturing method of a semiconductor device includes the steps of: preparing a lead frame; mounting a plurality of semiconductor chips on the lead frame; and sealing one portion of the lead frame with a sealing resin. The resin-sealing step includes the step of: disposing the lead frame, molds having main surfaces on which cavity parts are formed, the lead frame being disposed on the main surface of the heated molds; injecting a resin in the main surfaces of the heated molds so as to seal the one portion of the lead frame with the sealing resin; and taking out the lead frame from the heated molds. In the taking-out step, while the lead frame is taken out, the main surfaces of the molds are inspected by using a sensor, and the sensor is cooled and formed integrally with an arm used for taking out the lead frame.