A system for dehumidifying and drying a powder particle material has a drying hopper (21), a dehumidifying unit (30), and a circulation route having a processing gas supply route (40) and a processing gas dehumidifying route (41) that interconnect the drying hopper and the dehumidifying unit to allow processing gas to circulate. The system repeatedly supplies and circulates the processing gas in the circulation route. The processing gas supply route and the processing gas dehumidifying route are interconnected by a bypass route (44) having a regulation valve (45). A temperature sensor (47) for detecting the temperature of processing gas exhausted from the drying hopper is installed in the processing gas dehumidifying route. The system (A) further has control means (51) for controlling opening and closing of the regulation valve, provided in the bypass route, based on a temperature detection signal detected by the temperature sensor. The control by the control means (51) is performed under the condition that the total amount of circulation of the processing gas circulated in the circulation route, including the amount of the gas passing through the bypass route, is held substantially constant.