The present invention relates to a separation membrane including an organic polymer resin, in which a volume V1 of fine pores having a pore diameter of 100 nm or more is 0.3 cm3/g or more and 0.5 cm3/g or less, a volume V2 of fine pores having a pore diameter of less than 100 nm is 0.02 cm3/g or more and less than 0.1 cm3/g, and a ratio V1/V2 of the fine pore volume V1 to the fine pore volume V2 is 3 or more and 60 or less.