A hermetic compressor comprising: an electric element including a stator and a rotor that rotates relative to the stator; a compression element driven by the electric element; and a hermetic container that stores the electric element and the compression element, and accommodates lubricating oil, wherein the compression element includes: a shaft including a principal shaft to which the rotor is fixed and an eccentric shaft that is eccentric with respect to the principal shaft; a cylinder block including a bearing that rotatably supports the principal shaft and a cylinder having an inner space; a piston that reciprocates in the inner space; and a connection section that couples the piston to the eccentric shaft, and the piston includes: a columnar seal section in sliding contact with an inner peripheral face of the cylinder; two extension sections that have respective circular arc faces having the same radius as a radius of the seal section, are spaced in the circumferential direction, and extend from the seal section toward a bottom dead center side in the axial direction; and a columnar capture section that has a radius that is smaller than the radius of the seal section; characterized in that the columnar capture section further extends toward the bottom dead center side than the extension sections, and that a pin is provided which connects the connection section to the piston, wherein a length of the extension section is one half or more of, and three over two or less of a diameter of the pin. an electric element including a stator and a rotor that rotates relative to the stator; a compression element driven by the electric element; and a hermetic container that stores the electric element and the compression element, and accommodates lubricating oil, wherein the compression element includes: a shaft including a principal shaft to which the rotor is fixed and an eccentric shaft that is eccentric with respect to the principal shaft; a cylinder block including a bearing that rotatably supports the principal shaft and a cylinder having an inner space; a piston that reciprocates in the inner space; and a connection section that couples the piston to the eccentric shaft, and a shaft including a principal shaft to which the rotor is fixed and an eccentric shaft that is eccentric with respect to the principal shaft; a cylinder block including a bearing that rotatably supports the principal shaft and a cylinder having an inner space; a piston that reciprocates in the inner space; and a connection section that couples the piston to the eccentric shaft, and the piston includes: a columnar seal section in sliding contact with an inner peripheral face of the cylinder; two extension sections that have respective circular arc faces having the same radius as a radius of the seal section, are spaced in the circumferential direction, and extend from the seal section toward a bottom dead center side in the axial direction; and a columnar capture section that has a radius that is smaller than the radius of the seal section; a columnar seal section in sliding contact with an inner peripheral face of the cylinder; two extension sections that have respective circular arc faces having the same radius as a radius of the seal section, are spaced in the circumferential direction, and extend from the seal section toward a bottom dead center side in the axial direction; and a columnar capture section that has a radius that is smaller than the radius of the seal section; the columnar capture section further extends toward the bottom dead center side than the extension sections, and that a pin is provided which connects the connection section to the piston, wherein a length of the extension section is one half or more of, and three over two or less of a diameter of the pin.