A method of manufacturing a clutch housing which accommodates therein a plurality of clutch plates adapted to be engaged together so as to transmit a torque, wherein a drum portion and a boss portion can be integrally formed from a plate material so as to form a thick portion having a thickness of not less than approximately 1.3 times as large as that of the plate material and a thin portion having a thickness of not greater than approximately ½ of that of the plate material.