Provided is a method of manufacturing a toilet seat that is formed by joining together a seat front member and a seat rear member. The method includes a cutting step of forming a processed surface of a joint part between the seat front member and the seat rear member by cutting the joint part between the seat front member and the seat rear member with a cutting tool having a curved cutting blade part such that the shape of the processed surface is formed in a curved shape in which the seat rear member side thereof protrudes outward in a cross section perpendicular to the direction in which the joint part extends.