To provide a safety guard device for a joint mechanism capable of preventing a danger that a man is caught or kicked by the joint mechanism as much as possible, while maintaining functions of a machine having the joint mechanism.

A cover 1 is provided to cover the joint mechanism having a danger that a man is caught or kicked by the joint mechanism. Direction, dimension and shape of an opening part 3 of the cover are changed in response to movement of the joint mechanism to restrict exposure of the joint mechanism outside to the required minimum to secure safety.