[Object]To make it possible to firmly fix a mixing tip to a cartridge, and also remove the mixing tip from the cartridge by a simple operation.[Solution Means]A locking member locks a mixing nozzle coupled to a cartridge that includes two syringes, the mixing nozzle being configured to mix materials in a nozzle and discharge the materials, the locking member including a support rod supported by the mixing nozzle so as to be displaceable in a direction orthogonal to a direction in which the nozzle extends; a first engaging part that is engaged with one of two horizontal parts that are provided so as to be bridged across the two syringes; a second engaging part that is inserted in between the two horizontal parts and engaged with another one of the two horizontal parts; and an inclined part where the other end of the support rod is inclined toward the opposite side to the nozzle, the inclined part being provided in at least one of between the first engaging part and the second engaging part and between the second engaging part and the other end of the support rod.