A preform for a multi-layered hollow vessel has excellent moldability and productivity and is free from the deterioration of the characteristic properties of the vessel even when a recycled material is filled in large quantities. A molded product is produced by filling a first material and a second material into the cavity of an injection mold in a single molding step including (i) the substep of injecting the first material, (ii) the substep of injecting the first material and the second material at the same time and (iii) the substep of injecting the first material which are carried out continuously in this order.