This valve device (1A) contains the following: a main valve member (4) that partitions a valve-member space (20) inside a housing (2) into a first pressure chamber (32) and a second pressure chamber (24); and a pilot valve member (5) disposed inside the second pressure chamber (24). In one mode, a first pilot channel (61) that has a first diaphragm (62) extends from a primary channel (31) to the second pressure chamber (24) and a second pilot channel (63) that has a second diaphragm (64) is formed in the main valve member (4). The main valve member (4) and the pilot valve member (5) are coupled via a pin (8), with a gap (e1) formed between said pin (8) and either the main valve member (4) or the pilot valve member (5). The pilot valve member (5) opens and closes the second pilot channel (63) by means of a biasing element (55) and a drive mechanism (7). The main valve member (4) is designed such that a pressure differential between the first pressure chamber (32) and the second pressure chamber (24) drives said main valve member (4) in a direction whereby a secondary channel (32) is opened.
