A method and apparatus for manufacturing bent pipes of a composite material composed of resin and filling materials such as reinforcing materials and aggregates by employing a cylindrical molding tool which is deformable between straight-axis form and bent-axis form. Materials are supplied into the molding tool held in horizontally straight condition while the tool is rotated about a horizontal axis, and are molded into a pipe by centrifugal molding. Rotation of the tool is stopped when the pipe molded therein is in uncured state, then the tool is subjected to bending. The resulting bent pipe is removed after it is cured. Before the tool is bent, a bag made of a flexible sheet material is inserted into the pipe and inflated to straighten out the inner periphery of the pipe so as to protect the pipe from any possibility of deformation during bending operation. The molding tool is preferably made of such resilient material as rubber, is incased in a peripherally divisible frame or bellows-type flexible frame which, in turn, is suitably incased in a rotary frame. More preferably, the molding tool has a hollow space provided between its inner and outer walls; by filling liquid in the hollow space it is possible to achieve fine roundness in pipe molding irrespective of dimensional errors with the molding tool or frame.