The present invention provides a thermoelectric conversion material that comprises a nanopore-containing structure and has low thermal conductivity and an improved thermoelectric performance index. Said thermoelectric conversion material comprises a thermoelectric semiconductor layer formed on top of a block-copolymer substrate comprising a nanopore-containing block copolymer that comprises the following: a polymer unit (A) comprising a monomer for which the glass transition temperature of the homopolymer thereof is greater than or equal to 50 DEG C; and a polymer unit (B) comprising a conjugated diene polymer.