A thin film forming apparatus such that a substrate can be easily fixed/removed to/from the outer circumferential surface of a drum type substrate holder through a simple arrangement.The drum type substrate holder (5) is supported in a horizontal posture rotatably about a horizontal rotational shaft in a film deposition chamber A jig (13) holding a substrate (12) fixedly is transferred by an arm horizontally onto the outer circumferential surface of the drum type substrate holder (5), and an end part (13b) of the substrate fixing jig (13) can be secured by a securing device (14) provided at the corner part (5a) of the outer circumferential surface of the drum type substrate holder (5).