The plasma generator has the dielectric having the inner circumferential surface, and a pair of electrodes which are arranged separated from each other in the direction along the inner circumferential surface and are isolated from each other by the dielectric and which are capable of generating plasma on the inner circumferential surface by application of voltage. In the inner circumferential surface, at the positions between the pair of electrodes in a plan view, recessed portions causing electric field concentration are formed.