A biomass solid fuel manufacturing method, including: a heating step of carbonizing a biomass molded body formed by molding raw material biomass, in an external heating type rotary kiln, in which the rotary kiln includes a non-heating zone that is provided on an upstream side of a kiln body and is not provided with a heating unit on an outer circumference, the non-heating zone includes a spiral blade on an inner circumferential surface, and in the heating step, the biomass molded body is introduced to the non-heating zone of the kiln body.