A leakage of liquid inside a differential pressure detection device is reliably preventable. A diaphragm portion that detects a differential pressure as a pressure difference between a high pressure side and a low pressure side includes an annular member, a strain gauge provided in a hollow portion of the annular member, and a first plate and a second plate provided such that the annular member and the strain gauge are sandwiched. The first plate and the second plate each abut on a first annular packing. A first groove and a second groove (the first annular packing) overlap with the annular member when viewed from a first direction along an axis of the first hole.