A resin composition contains polylactic acid and a copolyester of lactic acid and another hydroxycarboxylic acid. The copolyester has a weight-average molecular weight of 11×104 or more. The copolyester has a copolymerization randomness of 0.5 to 3.0, the copolymerization randomness being calculated as a ratio (b/a) of a theoretical value (b) of a triad content of the other hydroxycarboxylic acid to a measured value (a) of the triad content of the other hydroxycarboxylic acid. The copolyester of lactic acid and another hydroxycarboxylic acid can be used as a soil biodegradation accelerator for accelerating soil biodegradation of polylactic acid.