Abstract: An oil supply structure of a chain saw comprises a pair of rail portions which are provided on the outer circumference of the main body of a guide plate, a guide groove which is formed between the two rail portions, a pair of oil supply holes which penetrate the two rail portions from outside and which open toward the guide groove, a through hole which penetrates the main body of the guide plate without any connection with the guide groove, and a pair of connection channels which connect outer end openings of each oil supply hole and two outer end openings of the through hole. Lubricating oil is supplied from an outlet port of the main body of the chain saw to both sides of a saw chain and so forth through the through hole, connection channel and oil supply hole.