An injection molding device includes an injection machine, a molding die, and a high frequency oscillation device. The injection machine injects a resin material containing a dielectric heat generating material while keeping fluidity by temperature control. The molding die includes a cavity being a channel of flow of the resin material, and a pair of electrodes, each of which faces the cavity, the pair of electrodes being disposed to sandwich the resin material therebetween in a direction crossing a direction of the flow. The high frequency oscillation device applies a high frequency alternate-current voltage to the pair of electrodes.