The valve device has a valve main body defining a valve chest provided with a NO outlet port and a NC outlet port through which a fluid flows, and a valve for opening/closing the NC outlet port and NO outlet port. The valve includes a diaphragm disposed so as to cover the valve chest, and a drive means for pressing the diaphragm to open/close the NC outlet port and NO outlet port. The first valve seat and the second valve seat are formed around the NC outlet port and NO outlet port. The diaphragm is made of an elastic material of which JIS-K6253 durometer A hardness is A50-A85. The pressure of the diaphragm seated on the first valve seat and the second valve seat is 0.5-1.0 N/sq·mm.