For the purpose of providing a particle beam therapy apparatus which is unnecessary to be separately verified for operational integrity of its dose monitors and is unnecessary to have an additional failure diagnosis function, a particle beam therapy apparatus (100) is so configured that, by a dose-monitoring system controller (54), the main and sub roles of two dose monitors (50, 51) are switched therebetween at every radiation and their corresponding dose monitor circuits (52, 53) are controlled accordingly, so that operation checking of the two dose monitors (50, 51) can be performed during a therapeutic flow, without the need of a special operation.