To provide a pump using a piezoelectric element vibration plate, correctly and accurately supporting the vibration plate and facilitating assembly of housing members.

A peripheral portion of a metal plate of the unimorph vibration plate 40 on a side facing the first housing member 14 is pressed and supported by a ridge portion of a circular protrusion 52 circularly formed along a periphery of a ventilation chamber 38. The first to third housing members 14, 16, 30 are lapped each other, the first and third housing members 14, 30 are welded each other by ultrasonic welding, and positional relations with each other of the housing members are determinately settled with the first and second housing members 14, 16 in a state of being butted to each other at abutments 66, 68 and with the second and third housing members 14, 30 in a state of being butted to each other at abutments 70, 72.