A crimping method of performing crimping to join an outer member to an inner member that is arranged inside the outer member, the method comprising: an inner-member preparation step of preparing the inner member that includes an insertion portion that has an outer circumferential surface having a shape of a columnar surface, and an annular groove provided in the outer circumferential surface; an outer-member preparation step of preparing the outer member that includes a main body portion, and a cylindrical portion that has a cylindrical shape and is continuous with the main body portion, and forms an opening into which the insertion portion is to be inserted; an insertion step of inserting the insertion portion into the cylindrical portion such that the insertion portion of the inner member is inserted into the cylindrical portion via the opening and a gap is provided between an inner circumferential surface of the cylindrical portion and the outer circumferential surface of the insertion portion; a diameter-reducing step (ST3, ST4) of reducing a diameter of the cylindrical portion with spinning such that a first reduced-diameter portion is formed so as to be located further inward in a radial direction than the main body portion due to plastic deformation of a first plastically-deformed portion and be continuous with the main body portion via said first plastically-deformed portion, and, then, of reducing a diameter of a part of the first reduced-diameter portion with spinning such that a second reduced-diameter portion is formed so as to be further inward in the radial direction than the first reduced-diameter portion and to be continuous with the first reduced-diameter portion via a second plastically-deformed portion, wherein at least a part of said second reduced-diameter portion has entered the annular groove provided in the outer circumferential surface of the inner member. an inner-member preparation step of preparing the inner member that includes an insertion portion that has an outer circumferential surface having a shape of a columnar surface, and an annular groove provided in the outer circumferential surface; an outer-member preparation step of preparing the outer member that includes a main body portion, and a cylindrical portion that has a cylindrical shape and is continuous with the main body portion, and forms an opening into which the insertion portion is to be inserted; an insertion step of inserting the insertion portion into the cylindrical portion such that the insertion portion of the inner member is inserted into the cylindrical portion via the opening and a gap is provided between an inner circumferential surface of the cylindrical portion and the outer circumferential surface of the insertion portion; a diameter-reducing step (ST3, ST4) of reducing a diameter of the cylindrical portion with spinning such that a first reduced-diameter portion is formed so as to be located further inward in a radial direction than the main body portion due to plastic deformation of a first plastically-deformed portion and be continuous with the main body portion via said first plastically-deformed portion, and, then, of reducing a diameter of a part of the first reduced-diameter portion with spinning such that a second reduced-diameter portion is formed so as to be further inward in the radial direction than the first reduced-diameter portion and to be continuous with the first reduced-diameter portion via a second plastically-deformed portion, wherein at least a part of said second reduced-diameter portion has entered the annular groove provided in the outer circumferential surface of the inner member. reducing a diameter of the cylindrical portion with spinning such that a first reduced-diameter portion is formed so as to be located further inward in a radial direction than the main body portion due to plastic deformation of a first plastically-deformed portion and be continuous with the main body portion via said first plastically-deformed portion, and, then, of reducing a diameter of a part of the first reduced-diameter portion with spinning such that a second reduced-diameter portion is formed so as to be further inward in the radial direction than the first reduced-diameter portion and to be continuous with the first reduced-diameter portion via a second plastically-deformed portion, wherein at least a part of said second reduced-diameter portion has entered the annular groove provided in the outer circumferential surface of the inner member.