Disclosed are a method and apparatus for controlling the injection rate of an anesthetic solution in a cartridge type motor-driven injection syringe for dental use, particularly beginning with the "Low" rate injection at the outset, and switching to the "Medium" or "High" injection rate at an arbitrarily selected time in the course of injection.
The speed of revolution of the electric motor is changed among the low, medium and high speed, and a two-step operable type of switch is used as a starter switch 13. The first depression of the starter switch makes the electric motor 9 start at the low speed, thereby making the plunger rubber 5 initially move at the "Low Speed" in the cartridge 6 via the plunger rod 12, and the second depression of the switch makes the electric motor 9 run at the low, medium or high speed, and accordingly the plunger rod moves at the selected "Low Speed", "Medium Speed" or "High Speed".