To provide a water circulating system for an ink swing roller of a printer easy to temperature control by stably holding a flow rate of a chilled water, supplying the water or a warm water to circulate the water as needed, and particularly early starting in winter.

A pressure regulating valve 10 is provided at a water circulating system between a pump 2 and ink swing rollers 1a, 1b. Further, a thermometer 8 and regulating valves 6a, 6b, 7a, 7b for controlling cooperatively with the thermometer 8 are provided to introduce the chilled water to the circulating system only in the case of high temperature of the circulating water of the rollers 1a, 1b. Moreover, a bypass for bypassing a water heater 9 is provided at the system, and the thermometer 8 and the valves for controlling opening/ closing of the bypass via the heater 9 cooperatively with the thermometer 8 are provided to heat the heater 9 only in the case of low temperature of the circulating water of the rollers 1a, 1b.