Abstract: A pressure detection apparatus capable of preventing an O-ring, which is sandwiched by a first case and a second case, from being squeezed to a gap between the first case and the second case. A pressure detection apparatus is formed by assembling a connector case as the first case, which includes a depression portion in which a sensor element is contained, and a housing as the second case. The housing includes a main body portion having a pressure introduce hole. A seal diaphragm and a press member are welded to the main body portion. A pressure detection chamber for containing oil is defined between the depression portion of the connector case and the seal diaphragm. At an outer peripheral portion of the pressure detection chamber, an O-ring is inserted to a groove formed at one end surface of the connector case. An outer peripheral portion of groove portion is defined as an outer peripheral wall. A corner portion is defined by a side surface and a contact surface of the outer peripheral wall.