When calibrating speed parameters of a switch characteristics tester, the calibration device must have a speed generator to provide speed signals. This paper describes design of a speed generator used for providing speed signals when calibrating switch characteristics testers. The design procedure is discussed. The device uses STM32F407 as MCU, and time reference is provided by the timer of it. The amplitude and pulse width of output pulsing signals can be customized. We choose spring as the energy storage element, and design a mechanical structure to provide real shift. Different speed signals can be chosen based on demands of calibrated instruments to provide speed signals for calibrating speed parameters of a switch characteristics tester.