PURPOSE: To provide the manufacturing method with low equipment cost of drain pipe, which is arranged in falling gradient so that unevenness is necessary on the inner surface for roughening the surface and made of fiber reinforced synthetic resin.

CONSTITUTION: The fiber reinforced synthetic resin pipe concerned consists of a mandrel 1, which is moved axially while being rotated peripherally, paper spacer 2, releasing film 4, resin-impregnated reinforcing fiber 5, resin mortar layer foring material 6 and resin-impregnated reinforcing fiber 7. Before winding the resin-impregnated reinforcing fiber 5 and the like round the mandrel 1, the spacer 2 is wound round the mandrel 1 so as to form tongued-and-grooved beads 3, 3... or the mandrel and, after that, the resin-impregnated reinforcing fibers are wound on the tongued-and-grooved beads 3, 3... and finally a resultant assembly is hardened so as to produce pipe body. Then, by removing the releasing film 4 and the spacer 2, the pipe body, on the inner surface of which tongued-and-grooved beads corresponding to the tongued-and-grooved beads 3, 3... are formed, is obtained.