This productivity evaluation method is for evaluating productivity of a chemical substance in a process comprising a first step of obtaining gas from a waste material and a second step of synthesizing a chemical substance from the gas obtained in the first step in the presence of a catalyst, said method including: a first carbon mass calculation stage of calculating mass of carbon contained in the waste material, a second carbon mass calculation stage of calculating mass of carbon contained in the chemical substance produced in said process, and a productivity evaluation stage of evaluating the productivity of the chemical substance based on values of the mass of carbon which are calculated in the first carbon mass calculation stage and the second carbon mass calculation stage.