A magnet generator including a bowl-shaped flywheel which is formed of a cylindrical portion and a bottom portion on one end side of the cylindrical portion, a plurality of magnets which are arranged on the inner peripheral surface of the cylindrical portion of the flywheel, and a power generation coil which generates power under an electromagnetic induction action with the magnets and which is disposed in opposition to the magnets within the flywheel, wherein the flywheel has a plurality of vent holes in its bottom portion, and the hole base part of each of the vent holes is formed in a droop or curved shape. Owing to the droop or curved shape, a cooling efficiency is enhanced, and a job for treating burrs and laps after cutting working can be relieved to enhance a productivity.