The present invention is directed to a mixing device 4 including: a mixing chamber 6 which defines a space for mixing a puncture repair liquid R and compressed air A; a first inlet 7 for supplying the compressed air A to the mixing chamber 6; a second inlet 8 for supplying the puncture repair liquid R to the mixing chamber 6; and an outlet 9 for discharging a mixture of the puncture repair liquid R and the compressed air A from the mixing chamber 6. The mixing chamber 6 includes an upper member 10 which defines a top surface 6a of the space, and a lower member 11 which defines a bottom surface 6b of the space, in a state of use. The second inlet 8 is formed in the upper member 10. The upper member 10 moves in a direction away from the bottom surface 6b due to supply of the compressed air A to provide communication between the second inlet 8, and the first inlet 7 and the outlet 9 via the mixing chamber 6, and moves toward the bottom surface 6b due to stop of the supply of the compressed air A to close the communication between the second inlet 8, and the first inlet 7 and the outlet 9.
