A bent pipe forming apparatus for extruding and forming a fluid material into an annular member having a central mandrel (22) and a die (21) defining an annular gap between the mandrel (22) and the die (21), wherein one of the mandrel (22) and the die (21) is supported to move in a direction perpendicular to an axis of the mandrel (22). The movable mandrel (22) or die (21) is provided on its outer periphery with a guide circular surface (XX) integral therewith. An inner movable ring (4) having inner and outer circular peripheries eccentric to each other is rotatably fitted on the guide surface. An outer movable ring (5) having inner and outer circular peripheries eccentric to each other is rotatably fitted on the periphery of the inner movable ring (4). The outer movable ring (5) is provided with an outer circular peripheries which is rotatably fitted in a stationary circular guide surface (YY). Driving motors (12a, 12b) are provided to independently move the inner and outer movable rings (4, 5).