A motive power transmission device comprising: a first motive power transmission member and a second motive power transmission member, the first motive power transmission member and the second motive power transmission member being rotatably provided in a motive power transmission path from a drive source to a drive wheel and being spline-fitted together; and a spring retaining member configured to retain a spring configured to urge the second motive power transmission member toward one side in a circumferential direction with respect to the first motive power transmission member, wherein the spring retaining member is mounted on the first motive power transmission member, and the spring retaining member includes a temporarily fixing portion, characterized in that: the temporarilly fixing portion is temporarily fixed to and mounted on the first motive power transmission member in a first compression state where the spring urges the spring retaining member toward the one side in the circumferential direction with respect to the first motive power transmission member; and in that the spring retaining member further includes a locking portion that is locked with the second motive power transmission member in a second compression state where when the first motive power transmission member and the second motive power transmission member are spline-fitted together, the spring is compressed more than the first compression state and urges the second motive power transmission member toward the one side in the circumferential direction with respect to the first motive power transmission member, the first motive power transmission member is provided with a temporarily fixed portion that is temporarily fixed to the temporarily fixing portion, and the second motive power transmission member is provided with a locked portion that is locked with the locking portion. a first motive power transmission member and a second motive power transmission member, the first motive power transmission member and the second motive power transmission member being rotatably provided in a motive power transmission path from a drive source to a drive wheel and being spline-fitted together; and a spring retaining member configured to retain a spring configured to urge the second motive power transmission member toward one side in a circumferential direction with respect to the first motive power transmission member, wherein the spring retaining member is mounted on the first motive power transmission member, and the spring retaining member includes a temporarily fixing portion, characterized in that: the temporarilly fixing portion is temporarily fixed to and mounted on the first motive power transmission member in a first compression state where the spring urges the spring retaining member toward the one side in the circumferential direction with respect to the first motive power transmission member; and in that the spring retaining member further includes a locking portion that is locked with the second motive power transmission member in a second compression state where when the first motive power transmission member and the second motive power transmission member are spline-fitted together, the spring is compressed more than the first compression state and urges the second motive power transmission member toward the one side in the circumferential direction with respect to the first motive power transmission member, the temporarilly fixing portion is temporarily fixed to and mounted on the first motive power transmission member in a first compression state where the spring urges the spring retaining member toward the one side in the circumferential direction with respect to the first motive power transmission member; and in that the spring retaining member further includes a locking portion that is locked with the second motive power transmission member in a second compression state where when the first motive power transmission member and the second motive power transmission member are spline-fitted together, the spring is compressed more than the first compression state and urges the second motive power transmission member toward the one side in the circumferential direction with respect to the first motive power transmission member, the first motive power transmission member is provided with a temporarily fixed portion that is temporarily fixed to the temporarily fixing portion, and the second motive power transmission member is provided with a locked portion that is locked with the locking portion.