Working method for end portion of plate member, manufacturing method for plate member, working apparatus for end portion of plate member, and plate member

A manufacturing method for a plate member formed of a thermoplastic resin, comprising:

• cutting the plate member into a predetermined shape;
• and
• a first working process of heating and pressing an end portion of the plate member in a thickness direction to form a thin portion, the thin portion being formed such that a pressed surface of the thin portion has a recessed portion at a position adjacent to an inner end of the thin portion on an inner side of the plate member, a second working process of folding the thin portion to move an outer peripheral end of the thin portion on an outer peripheral side of the plate member to a vicinity of a main body portion of the plate member to which the inner end of the thin portion is connected, and a third working process of pressing an outer surface of a first portion of the outer peripheral end of the thin portion in the thickness direction to move the outer peripheral end of the thin portion further inward than a surface of the main body portion in the thickness direction, such that the outer surface of the first portion of the outer peripheral end is moved further inward in the thickness direction than an outer surface of a second portion of the outer peripheral end.