To process a turbine shell at low cost by drawing a disc plate into a curved and recessed shape after a plurality of plate fixing slits have been punched out of the flat disc plate when the turbine shell of a torque converter is processed.

A curved and recessed shaped turbine shell 10 to be used for the turbin of a torque converter, is formed out of a drawn and curved part 30 in a curved arc shape in cross section, and of a ring shaped stationary part 31. In case of processing the turbine shell 10 as described above, a circular shaped blank 40 is punched out of a sheet metal, and concurrently a center hole is thereby formed. Subsequently, a plurality of plate fixing slits are simultaneously punched out of the flat blank 40, in this case, the wide of each slit is made wider in the order of each outer circumferential slit 32C, each intermediate slit 32B and each inner circumferential slit A. Next after the drawn and curved part 30 and the ring shaped stationary part 31 have been formed over the blank 40 by means of drawing works, riveting holes 33 are formed in the ring shaped stationary part 31 by means of pierce processing.