To provide a wood crusher and a tension imparting mechanism capable of preventing fall of a belt body (chain or belt) and idling of a tab, even if normal rotation and reverse rotation of the tab are repeated.

The wood crusher 10 rotates the tab 2 by winding a chain 11 around the outer periphery of the tab 2, and rotating a sprocket 31 meshed with the chain 11 by a driving motor M, and is provided with the tension imparting mechanism 40 imparting tension to the chain 11 wound around the outer periphery of the tab 2. The tension imparting mechanism 40 is provided with an elastic member 41 generating elastic force for pulling a part of the chain 11, and abutting parts 42d, 47d restricting elongation of the elastic member 41 beyond a given amount.