PURPOSE: To improve the release properties of a sheet material by a method wherein a forming female die to manufacture the bottom material of a carriage body, on which a large number of embossed parts to contain electronic components are provided, is constituted of a female die main body and an embossed bottom part constituting member, which is movably provided in the female die main body.

CONSTITUTION: For a forming device 15 to form a bottom material by forming multiple rows of embossed parts, a large number of which are provided in the carrying direction at a specified pitch, a female die main body 32a for a forming female die 32 is moved upward at the time of sheet material forming, and a sheet plate 51 is pressed to a forming male die 34. Then, stems 37 are pressed downward, and a bottom part supporting body 35, which is integrated with the stems 37, is lowered while resisting a spring 38. Under such condition, a protuberance supporting body 41 of the forming male die 34 is lowered by a driving mechanism, and embossed parts are formed on the sheet plate 51 by inserting embossing protuberances 42 in embossing grooves 36. After the forming, when the protuberance supporting body 41 is raised and the female die main body 32a is lowered, the bottom part supporting body 35 is raised by springs 38, and the sheet plate 51 is released from the dies.