A valve device of the present invention includes: a main valve body interposed between a first pressure chamber of a main passage and a second pressure chamber; and a pilot valve body provided in the second pressure chamber. A first pilot passage including a first restrictor extends from an outside of a housing or a primary passage to the second pressure chamber, and a second pilot passage including a second restrictor is formed at the main valve body. The pilot valve body is maintained at a first operation position by a pilot valve body biasing member and is caused to move to a second operation position by a valve body driving unit. When the pilot valve body is located at the second operation position, the main valve body is caused to move to an open position by a pressure difference between the first pressure chamber and the second pressure chamber.