Disclosed are a medical instrument and a medical material each comprising an aliphatic polyester resin composition, which are hardly reduced in strength and impact resistance upon the sterilization by ionizing radiation or have excellent shape-retaining properties after a heat treatment. Specifically, a medical instrument and a medical material both sterilized by ionizing radiation are provided, each of which contains a biodegradable resin and a polycarbodiimide compound in an amount of 0.1 to 10% by weight on the resin. The biodegradable resin is polybutylene succinate, a copolymer of polybutylene succinate, or a mixture of polybutylene succinate and a copolymer of polybutylene succinate with polylactic acid or poly(3-hydroxyalkanoate). A method of producing such medical instrument and medical material is also provided.