Method of manufacturing resin molding and change-over device for changing over between heating medium and resin material in process of secondary forming

The change-over device changes over, to one of three passages, between the runner groove connected to the injection nozzle and the communicating groove communicated with the mold side passage. At the first position, the second passage is communicated with the communicating groove and the temperature of a flow of hot air is measured by the thermocouple and the flow is discharged into the atmosphere. At the second position, the runner groove and the communicating groove are communicated with each other when the runner groove and the communicating groove are open to the second passage and resin material is injected into the mold. At the third position, the material in the injection passage and the material in the runner groove are deposited to each other when the injection passage is shut off from the communicating passage and the third passage is communicated with the runner groove.