A locking member that locks a mixing nozzle to a cartridge that includes two syringes, the mixing nozzle being configured to mix the materials from the two syringes within the nozzle as the materials are discharged. The locking member includes a support rod supported on the mixing nozzle that is displaceable in a direction orthogonal to the direction in which the nozzle extends, and first and second engaging parts that engage with horizontal parts provided on the cartridge. The locking member further includes an inclined part that is inclined toward the opposite side to the nozzle, and that is provided between at least one of the first engaging part and the second engaging part, or between the second engaging part and the other end of the support rod.