A locking member that locks a mixing nozzle coupled to a cartridge that includes two syringes accommodating different materials, the mixing nozzle being configured to mix the materials pushed out from the two syringes in a nozzle and discharge the materials, the locking member comprising: 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 protrudes from one end of the support rod toward an opposite side to the nozzle, and that is displaced toward another end of the support rod to be engaged with one of two horizontal parts (503, 504) that are provided so as to be bridged across the two syringes; a second engaging part that protrudes from a position of the support rod that is closer to the other end of support rod than the first engaging part, toward the opposite side to the nozzle, and that is inserted in between the two horizontal parts (503, 504) and displaced toward the other end of the support rod to be engaged with another one of the two horizontal parts (503, 504); and an inclined part (421, 422) where the other end of the support rod is inclined toward the opposite side to the nozzle, characterized in that the inclined part (421, 422) is provided as a first inclined part that is provided between the first engaging part and the second engaging part, and a second inclined part that is provided between the second engaging part and the other end of the support rod, wherein each of the first inclined part and the second inclined part includes an upper end side inclined part (421a, 422a) that is inclined by a first inclined angle (α) with respect to the direction in which the nozzle extends, and a lower end side inclined part (421b, 422b) that is inclined by a second inclined angle (β), smaller than the first inclined angle (α), with respect to the direction in which the nozzle extends. 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 protrudes from one end of the support rod toward an opposite side to the nozzle, and that is displaced toward another end of the support rod to be engaged with one of two horizontal parts (503, 504) that are provided so as to be bridged across the two syringes; a second engaging part that protrudes from a position of the support rod that is closer to the other end of support rod than the first engaging part, toward the opposite side to the nozzle, and that is inserted in between the two horizontal parts (503, 504) and displaced toward the other end of the support rod to be engaged with another one of the two horizontal parts (503, 504); and an inclined part (421, 422) where the other end of the support rod is inclined toward the opposite side to the nozzle, characterized in that the inclined part (421, 422) is provided as a first inclined part that is provided between the first engaging part and the second engaging part, and a second inclined part that is provided between the second engaging part and the other end of the support rod, wherein each of the first inclined part and the second inclined part includes an upper end side inclined part (421a, 422a) that is inclined by a first inclined angle (α) with respect to the direction in which the nozzle extends, and a lower end side inclined part (421b, 422b) that is inclined by a second inclined angle (β), smaller than the first inclined angle (α), with respect to the direction in which the nozzle extends. an upper end side inclined part (421a, 422a) that is inclined by a first inclined angle (α) with respect to the direction in which the nozzle extends, and a lower end side inclined part (421b, 422b) that is inclined by a second inclined angle (β), smaller than the first inclined angle (α), with respect to the direction in which the nozzle extends.