PURPOSE: To enable the opening and closing to be performed smoothly and elevate the accuracy in mold setting by heating upper and lower molds to a sealing temperature and heating a lower platen with a heater before loading lead frames into a resin-sealing device.

CONSTITUTION: An upper mold 1 and a lower mold 5 are heated to a sealing temperature and a lower platen 4 is heated with a heater 11 before loading lead frames 8 into a lower mold 5. When heating the lower platen 4, the temperature of the upper platen 2, the temperature of a mobile platen 6, and the temperature of a tie bar 3 are detected by temperature sensors 13-15, and the calorific value of the heater 11 is always controlled so that the temperature of the lower platen 4 may come close to those temperatures. After the upper and lower molds 1 and 5 are heated to specified temperatures, a tablet 10 and a lead frame 8 are loaded on the lower mold 5. And, in the same way as before, the mold is released and a product is taken out after going through a clamping process, a resin injection process, and a resin hardening process.