To provide an air vent valve which is made difficult to generate a situation that an outflow port can not be closed due to jamming of foreign matter and a piping structure provided with the air vent valve.

An air vent valve 70 is provided with a ball type valve element 73, a valve chamber 72 storing the valve element 72 so that the element 73 may be floated, an inflow port 74 flowing fluid into the valve chamber 72 and an outflow port 75 flowing fluid out of the valve chamber 72. In an upper part within the valve chamber 72, a valve seat 76 is formed. By floating the valve element 73 by the pressure of liquid flowing from the inflow port 74 into the valve chamber 72 and seating the floating up valve element 73 on the valve seat 76, the outflow port 75 is constituted so as to be closed.