A pump apparatus includes a piezoelectric pump, an outer housing, and an adhesive sheet. The piezoelectric pump has a principal surface at which a discharge port for a fluid is formed. The outer housing has a housing channel that communicates with the discharge port, and the outer housing is formed at least partially using a resin having water-containing properties. The adhesive sheet adheres the principal surface of the piezoelectric pump to the outer housing. The outer housing includes a main plate. The main plate has a principal surface that opposes the principal surface of the piezoelectric pump and is in contact with the adhesive sheet. The main plate also has a through-hole that communicate with the discharge port and with the housing channel. The principal surface is formed as a surface of a metal portion.