PURPOSE: To carry out laminate injection moulding with one device easily by inserting a heat source into a cavity mould, connecting vacuum system or a compressed air system to the mould and vacuum (compressed air) forming a sheet, and then modifying this forming machine into an injection moulding machine.

CONSTITUTION: A synthetic resin sheet 10 is sandwiched between cavities 1 formed by a pair of moulds 2 and 3, a sheet forming die 7 is set in one mould 2 of the cavities 1, radiating heat sources 13 are set in the other mould 3, a vacuum system or a compressed air system 11, 14 is attached to these moulds 2 and 3, and the sheet 10 is vacuum formed or compressed air formed. Next, this forming die is assembled for injection moulding by an ordinary method and loaded on an injection moulding machine, the heat formed sheet 10 is loaded in it, and laminate injection moulding is carried out.