A system comprising a rivet fastening air tool and rivets, each of the rivets comprising: a female member having a base portion; a leg portion extending from the base portion, the leg portion being inserted in an attachment bore provided in an attachment side, and bent on a rear face side of the attachment bore so as to be able to expand a diameter of the leg portion; and a communicating bore communicated from the base portion to the leg portion; and a male member having a head portion; and a shaft portion extending from the head portion, the male member being inserted into the communicating bore to be able to be pulled out, and opening the leg portion by moving the shaft portion in a direction of being pulled out of the communicating bore; wherein multiple rivets are attached together to form a rivet row by connecting adjacent head portions through fragile portions such that the leg portions face a same direction; and the rivet fastening air tool comprising: a supplying actuator for loading the rivet row, the supplying actuator tearing off a fragile portion of a very front-row rivet and supplying the rivet in a loaded position; an knocking actuator retaining the head portion of the rivet supplied in the loaded position, and moving the rivet in a direction of being pulled out of the communicating bore; characterized in that the rivet fastening air tool comprises a switching valve provided in an air supply route which reaches the supplying actuator, wherein when the head portion of the rivet is moved in the direction of being pulled out, the switching valve is switched by the knocking actuator so that the supplying actuator is returned in a counter-transfer direction, wherein the rivet fastening air tool further comprises a switching shaft, wherein one end portion of the switching shaft is fitted into the switching groove of the main shaft, and the other end portion of the switching shaft is connected to a piston rod of the switching valve, and wherein, in use, when the main shaft moves backward, the switching shaft is pushed by the end face of the switching groove, so that the switching valve is switched. a female member having a base portion; a leg portion extending from the base portion, the leg portion being inserted in an attachment bore provided in an attachment side, and bent on a rear face side of the attachment bore so as to be able to expand a diameter of the leg portion; and a communicating bore communicated from the base portion to the leg portion; and a male member having a head portion; and a shaft portion extending from the head portion, the male member being inserted into the communicating bore to be able to be pulled out, and opening the leg portion by moving the shaft portion in a direction of being pulled out of the communicating bore; wherein multiple rivets are attached together to form a rivet row by connecting adjacent head portions through fragile portions such that the leg portions face a same direction; and the rivet fastening air tool comprising: a supplying actuator for loading the rivet row, the supplying actuator tearing off a fragile portion of a very front-row rivet and supplying the rivet in a loaded position; an knocking actuator retaining the head portion of the rivet supplied in the loaded position, and moving the rivet in a direction of being pulled out of the communicating bore; characterized in that the rivet fastening air tool comprises a switching valve provided in an air supply route which reaches the supplying actuator, wherein when the head portion of the rivet is moved in the direction of being pulled out, the switching valve is switched by the knocking actuator so that the supplying actuator is returned in a counter-transfer direction, wherein the rivet fastening air tool further comprises a switching shaft, wherein one end portion of the switching shaft is fitted into the switching groove of the main shaft, and the other end portion of the switching shaft is connected to a piston rod of the switching valve, and wherein, in use, when the main shaft moves backward, the switching shaft is pushed by the end face of the switching groove, so that the switching valve is switched. a supplying actuator for loading the rivet row, the supplying actuator tearing off a fragile portion of a very front-row rivet and supplying the rivet in a loaded position; an knocking actuator retaining the head portion of the rivet supplied in the loaded position, and moving the rivet in a direction of being pulled out of the communicating bore; characterized in that the rivet fastening air tool comprises a switching valve provided in an air supply route which reaches the supplying actuator, wherein when the head portion of the rivet is moved in the direction of being pulled out, the switching valve is switched by the knocking actuator so that the supplying actuator is returned in a counter-transfer direction, wherein the rivet fastening air tool further comprises a switching shaft, wherein one end portion of the switching shaft is fitted into the switching groove of the main shaft, and the other end portion of the switching shaft is connected to a piston rod of the switching valve, and wherein, in use, when the main shaft moves backward, the switching shaft is pushed by the end face of the switching groove, so that the switching valve is switched.