A method of forming bottomed cylindrical bodies, which can be used conveniently as preforms for the production of containers by stretch blow-molding, etc., from a cylindrical body of thermoplastic resin. The method includes a softening step of heat-softening an axially intermediate part of the cylindrical body, a necking step of necking the axially intermediate part of the cylindrical body radially inwardly, said necking step being carried out subsequently to, or simultaneously with, the softening step, a cutting step of cutting the axially intermediate part of the cylindrical body necked radially inwardly in the necking step, thereby to divide the cylindrical body into two members, and a fusing step of heat-melting the cut end portion of each of the two members and fusing the cut end portion.