Accelerating cavity and accelerator

An accelerator comprising:

• an accelerating cavity, wherein, the accelerating cavity comprises;
• a housing having an inner peripheral surface in a tubular shape and conductivity on a surface;
• and
• a plurality of cells provided inside the housing and each made of a dielectric including, at a central part, an opening through which a charged particle passes, wherein
• the housing includes a barrel portion having a tubular shape and end plates installed at both ends of the barrel portion, the plurality of cells are disposed in a range extending from the end plate on one end side of the housing to the end plate on the other end side, and
• each cell includes:
• a cylindrical barrel portion having a diameter smaller than an inner diameter of the barrel portion of the housing;
• and
• a plate portion provided inside of the cylindrical barrel portion to be fixed to the cylindrical barrel portion, and disposed such that a plate surface is orthogonal to a passing axis of the charged particle, and provided with the opening.