A shock absorption device of a safety plate for a grass mower includes: an upper safety plate support member formed at the upper portion of a safety plate for supporting a blade and a lower safety plate support member coupled to the upper safety plate support member for supporting the safety plate. Safety plate rotation-restraining means are formed to correspond to each other on an inner periphery of a through hole of the safety plate and an outer periphery of the upper safety plate support member or the lower safety plate support member, and a rotation preventing die is fixed to a handle in order to prevent the rotation of the lower safety plate support member.
