An ignition system for an internal combustion engine includes two power transistors respectively connected to opposite ends of the primary winding of an ignition coil to interrupt the primary currents which flow from a power source through the mid-tap of the primary winding. The two power transistors have emitters connected in common and a resistor is connected to the junction of this common connection to detect respective primary currents with the single resistor. A single current control circuit is provided to control the two power transistors in response to the detected respective primary currents.