A rotary compressor includes a compression mechanism having a cylinder, a piston, and a Helmholtz muffler. The Helmholtz muffler has a resonance chamber in the compression mechanism and a communication groove formed on an end face of the cylinder to connect the cylinder and resonance chambers. The communication groove is open at the end face of the cylinder and has a pair of side wall portions and a bottom wall portion between the side wall portions. Each side wall portion has a first portion adjacent an open end of the communication groove and a second portion adjacent the bottom wall portion. A surface of the first portion is a flat or bowed surface. A surface of the second portion is a bowed surface having a predetermined curvature so as to be connected to the surface of the first portion and a surface of the bottom wall portion.