To produce a crosslinked polyolefin foam excellent in softness with a simple apparatus while solving the problems with flowability of resin and adhesion of resin to a substrate by unidirectionally foaming at least a part of a polyolefin sheet.

One or two surfaces vertical to the foaming direction of a polyolefin sheet is bonded to a substrate in advance and the sheet is unidirectionally foamed. Pref., a polyolefin, the starting material, is subjected to a corona discharge treatment in advance to promote adhesion to the substrate. The starting material is pref. a compsn. contg. at least 20 wt.% essentially linear ethylene homo- or copolymer having a density of 0.80-0.96 g/cm3. The surface appearance of the resultant product can be adjusted as desired according to the application. The surface may consist of the substrate or may be the surface of the foam itself after separated from the substrate.