PURPOSE: To enhance the yield of a foamed soft polyurethane foam product by making mutually opposed foaming side plates and mutually opposed vulcanizing rollers parallel on both fixed and movable sides so as to make the interval between them same to foaming width.

CONSTITUTION: A foaming fixed side plate 2, a foaming movable side plate 3, a plurality of fixed vulcanizing rollers 4 and a plurality of movable vulcanizing rollers 5 are parallelly erected on an endless conveyor 1 at a right angle in a noncontact state. Paper is continuously laid on the conveyor 1 to be brought into contact with the side plates 2, 3 from the lower ends thereof toward the upper ends thereof and soft polyurethane foam is produced on the paper laid on the conveyor 1 so as to be held between the side parts of the paper by foaming and curing the polyrethane raw material sprinkled over the conveyor 1. When foaming width is increased, the foaming movable side wall 3 and the vulcanzing rollers 5 are intermittently increased by definite width at the same time until the foaming width becomes predetermined width. The side surface papers covering the side surfaces of polyurethane foam are advanced by foaming pressure without slipping down along the side plates 2, 3 and the rollers 4, 5. At the time of the increase of the foaming width, the emitting amt. of polyurethane foam is increased and decreased corresponding to width increasing quantity. Therefore, the increase of width can be smoothly performed and efficiency is enhanced.