PURPOSE: To simply and certainly measure the distortion of an oval plastic pipe.

CONSTITUTION: Centering jigs 2, 3 are provided to both end parts of a plastic pipe 1 having an oval cross section wherein large and small diameter circular arcs are connected by a gentle curve and a transmitter 4 and a receiver 5 are attached to the support levers erected along the center lines of the centering jigs 2, 3. The signal transmitted from the transmitter 4 is received by the receiver 5 and the positional shift of the center lines L1, L2 connecting the center point O1 of the large diameter circular arc and the center point O2 of the small diameter circular arc at both end parts of the plastic pipe 1 is measured. Therefore, the distortion of the oval plastic pipe 1 can be simply and certainly measured.