To easily control the elution of a biologically active substance in a granular composition consisting of a granular substance containing a biologically active substance which is coated with a biodegradable resin film.

A urethane resin having a Young's modulus of 100 MPa or less is used as a resin for coating a granular substance containing a biologically active substance and an organic iodine compound having a water solubility of 1,000 ppm or less and/or an isothiazoline compound having a water solubility of 1,000 ppm or less is used as an antimicrobial agent. The antimicrobial agent of 0.0001-1 pts.wt. to 100 pts.wt. of the granular composition is made to exist on the surface of the coating film.