Disclosed is an adhesive film having high dimensional stability which can be suitably used for two layer FPCs. Specifically, disclosed is an adhesive sheet composed of an insulting layer and an adhesive layer arranged on one side or both sides of the insulating layer. This adhesive sheet is characterized in that the insulating layer has a ratio E′2/E′1 between the storage elasticity modulus E′1 at 25° C. and the storage elasticity modulus E′2 at 380° C. of not more than 0.2 and a coefficient of thermal expansion in the MD direction of 5-15 ppm at 100-200° C. It is further characterized in that the change in the coefficient of thermal expansion of the adhesive sheet at 100-250° C. after heat treatment at 380° C. for 30 second under tension of 20 kg/m is not more than 2.5 ppm in the tension direction and not more than 10 ppm in the direction perpendicular to the tension direction.