Provided is a valve mechanism which has a simple configuration, being available for a type having a large bore diameter, and being able to be opened in response to extremely high temperature to supply fire-fighting water or cooling water. There is provided a valve mechanism opened in response to extremely high temperature, the valve mechanism including: a cylindrical body that is attached to an end of a supply pipe connected to a water source; a stopper that blocks a channel inside the body; a support that is disposed inside the body and that supports the stopper by pressing the stopper to a side of the supply pipe; a locking unit that serves to lock the support in a normal state and that unlocks the support in the case of extremely high temperature; and a heat sensitive section that releases the locking unit in the case where temperature of environment is increased to an extremely high level.