To provide a motion toy which has an unexpected nature and is rich in humor.

The motion toy comprises: a shell body, which has two or more shell pieces placed side by side and is composed so that the adjoining shell pieces are flexibly connected each other and that a degeneration state, which is in a round state, and a developed state, which is in an opened state, could be taken by expansion and contraction; and an biasing means which brings the shell body into the degeneration state by biasing force, wherein a deployment means is prepared in the one aspect side of the shell body, and the deployment means is composed so that the shell body transiently and intermittently takes the developed state by pressing the shell body from the one aspect side in opposition to the biasing force by the biasing means.