A mounting structure for a pressure sensor serves to facilitate easy attachment of the pressure sensor as well as easy detachment thereof without requiring any large work space. A pair of elastic snap fit portions (8) are formed on a surge tank (4) so as to protrude from a surface thereof, and have engagement protrusions (8a) formed at their one end, respectively, so as to protrude to a side opposite to a case (2). A pair of engaged portions (2b) are formed on the case (2) so as to be engaged with the engagement protrusions (8a), respectively. The snap fit portions (8) are forced to flexibly deform to the pressure sensor (1) when the pressure sensor (1) is attached to and detached from the surge tank (4).