An RF accelerating cavity includes: a housing having an inner peripheral surface in a tubular shape and conductivity at least on a surface; and accelerating cells inside the housing and each made of a dielectric including, at a central part, an opening through which a charged particle passes. The housing includes a cylindrical barrel portion, with end plates at both ends. The accelerating cells are disposed between the end plates. Each accelerating cell includes: a cylindrical barrel portion having a diameter smaller than an inner diameter of the cylindrical barrel portion of the housing; and a circular disk portion provided inside the cylindrical barrel portion to be fixed to the cylindrical barrel portion, and disposed such that a plate surface is orthogonal to the passing axis of a charged particle, and provided with the opening.