PROBLEM TO BE SOLVED: To provide a syringe that is hardly broken even when a liquid having a high viscosity is injected with high pressure, and a cylinder holder and a medical solution injection system using the syringe and the syringe holder.SOLUTION: The syringe is mounted in a cylinder holder for holding a flange of the syringe by a cylinder holder groove and fixing the syringe, and can be used as an injection device. The cylinder holder is provided with a positioning mechanism fitted to a recessed part, and the syringe has a recessed part fitted to the positioning mechanism.SELECTED DRAWING: Figure 5