To easily manufacture relatively long and hollow plastic imitation wood having an excellent hollow shape, being light in weight and excellent in durability and also having holes for connection formed integrally.

A mandrel 28 is inserted along the longitudinal direction into a cavity 25 of a mold 6 wherein the long cavity 25 for molding imitation wood is formed. Molten resin is t injected into the cavity 25 of the mold 6 in a state wherein the fore end part of the mandrel 28 is held by end part supports 80 fitted inside the cavity 25 of the mold 5 so that they can be moved back and force in the direction perpendicular substantially to the longitudinal direction. After the molten resin is filled inside the mold 6, the end part supports 80 are moved back from the cavity 25 of the mold 6 before the resin is set completely. The mandrel 28 is extracted thereafter along the longitudinal direction of the cavity 25 and cooling of the resin in the cavity 25 of the mold is continued.