The injection molding device of the present invention is provided with a supply pipe which supplies a heat medium to a mold, a discharge pipe which discharges the heat medium from the mold, a mold temperature adjustor to which the supply pipe and the discharge pipe are connected to adjust the temperature of the mold, and a discharge rate adjusting unit which is provided with a variable flow control valve installed on the discharge pipe to adjust a flow rate of the heat medium, a discharge pipe variable flow control valve bypass pipe for bypassing the variable flow control valve and a discharge pipe bypass on-off valve installed on the bypass pipe to change a flow rate of the heat medium and which is installed at a position upstream from the mold temperature adjustor on the discharge pipe.