Provided is a crosslinked polyolefin resin foam which is flexible and exhibits excellent sealing properties. The crosslinked polyolefin resin foam is characterized in that: when a C 4-12 a-olefin-copolymerized, linear, low-density polyethylene resin is referred to as "a resin (Y)", and a low-density polyethylene resin other than the resin (Y) is referred to as "a resin (X)", the content of the resin (X) is lower than that of the resin (Y); the sum total of the resin (X) and the resin (Y) is 50 to 100 mass% relative to 100 mass% of all the components of the foam; the 50% compressive hardness is 70kPa or less; when the foam is divided in the thickness direction into equal four parts, namely, foam layer (A), foam layer (B), foam layer (C) and foam layer (D) in this order from one face side of the foam, and the 50% compressive hardnesses of the foam layers (A) and (D) are referred to as "compressive hardness (a)" and "compressive hardness (d)" respectively, the ratio of the compressive hardness (a) to the compressive hardness (d) is 1/20 to 1/2; and the air permeability in the thickness direction is less than 0.9L/min.