A rotatably supporting structure is composed in combination of a raised portion and its matching annular recess. The raised portion is provided on either the outer circumferential surface of a shaft, which is adapted to be fixed at one end thereof on a fixed part, or the inner circumferential surface of a central bore of a member to be supported rotatably. The annular recess is formed in either the outer circumferential surface or the inner circumferential surface and is adapted to receive the raised portion therein. A tapered or curved surface is formed on at least one of the raised portion and a portion of the shaft or rotatably supported member defining the annular recess, which portion is brought into contact with the raised portion upon assembly of the rotatably supporting structure. The rotatably supported member is supported at both sides of the raised portion.