Abstract: In a heating/cooling unit for selectively heating or cooling a set of dies, oil received in a reservoir is supplied to a flow direction changeover valve by a first oil pump. In a stably mode, oil is returned to the reservoir through the changeover valve and a heat exchanger. In a heating mode, the oil is supplied to a second oil pump from the changeover valve through a check valve. The second oil pump supplies the oil to an oil heater, and the heated oil is introduced into a fluid path formed in the dies to heat the dies. The oil discharged from the fluid path of the dies is returned to the second oil pump. Thus, the heated oil is circulated in a closed loop in the heating mode. In a cooling mode, new oil is supplied to the fluid path of the dies from the changeover valve and the oil discharged from the fluid path is guided to the heat exchanger through a switching valve and the cooling oil is returned to the reservoir.