A particle detecting apparatus has a condensing and growing unit to condense and grow a condensing component over particles contained in a gas while the gas imported through an inflow port is transported from a low temperature portion to a high temperature portion, a particle detector to detect a concentration of the particles contained in the gas discharged from an outflow port of the condensing and growing unit, a particle feeder to feed, to the inflow port of the condensing and growing unit, a test gas containing test particles whose particle diameter and the number of particles per unit volume are known, and a first determinator to determine whether a concentration of the test particles contained in the test gas detected by the particle detector has a predetermined value.