To provide a valve structure and an emergency release mechanism of a parking brake, capable of opening and closing a flow channel by a simple structure and reducing a manufacturing cost.

A plug 31 has a head 33 projecting to the external of a housing 4, and a shaft 34 inserted into an opening formed at the housing 4 and screwed to the housing 4, and movable between an opened position for opening the flow channel and a closed position located at the axial tip side of the shaft 34 with respect to the opening position, for closing the flow channel. A spacer 32 is detachably mounted between the head 33 of a plug 31 and the housing 4. In this emergency valve 10, the plug 31 is retained on the opened position by fastening the plug 31 in a state of placing the spacer 32 between the head 33 of the plug 31 and the housing 4, and the plug 31 is retained on the closed position by fastening the plug 31 in a state of not placing the spacer 32 between the head 33 of the plug 31 and the housing 4.