The invention discloses a mechanical supercharger which comprises a gear transmission member used to transfer power, wherein the gear transmission member comprises a transmission shaft, a first transmission gear assembled on the transmission shaft, and a second transmission gear; the transmission shaft is connected with a crankshaft, and is sleeved with a supercharger impeller shaft; the supercharger impeller shaft is sleeved with a supercharger impeller and a diffuser; the diffuser is fixed to a casing; and the second transmission gear is assembled on the diffuser, and is engaged with the first transmission gear and the supercharger impeller shaft, in order to transfer the power transferred to the first transmission gear by the transmission shaft to the supercharger impeller shaft with drive the supercharger impeller to rotate. The mechanical supercharger adopts the gear transmission member to transfer the power, so that when the mechanical supercharger transfers the power, the transfer power, the transfer speed and the transfer ratio are high; the transmission efficiency is high; the structure is compact during mounting; the operation is stable and reliable; the service life is long; the transmission smoothness is high; and the transfer movement is accurate and reliable.