Saccharomycopsis fibuligera immobilized within agarose gel beads extracellularly produces glucoamylase, with which concanavalin A can aggregate to form a concanavalin A-glucoamylase complex. The complex increasingly accumulates in the gel beads with increasing glucoamylase production in the presence of concanavalin A. The formation or degradation of the complex is controlled in response to the presence or absence of methyl-alpha-D-mannopyranoside, which has a higher affinity toward concanavalin A. Gluco amylase was harvested with high recovery and purity by adding methyl-alpha-D-mannopyranoside.