An object of the present invention is to provide a soft biomass decomposition method, a production method for a target substance from soft biomass, and an enzyme or group of enzymes for decomposing soft biomass. Provided is a soft biomass decomposition method, including a step of bringing an enzyme selected from specific exocellulase, endocellulase, and processive endocellulase into contact with soft biomass such as bagasse and rice straw. Also provided is a production method for a target substance from soft biomass by incorporating the soft biomass decomposition method as a step. Further provided is an enzyme or group of enzymes for decomposing soft biomass selected from specific exocellulase, endocellulase, and processive endocellulase.