The temporal and spatial distributions of a magnetically driven shunting arc plasma were obtained using time-resolved probe measurement. A shunting arc was produced using a carbon rod and accelerated along a pair of rail electrodes by a Lorenz force. The pulse current for driving and maintaining the plasma was supplied from a 20 μF capacitor charged by a dc power supply. Double and single probes were employed to obtain the ion density of the shunting arc plasma. An ion density of 1 × 1019m-3 was obtained at a distance of 50mm from the carbon rod 15 μs after applying voltage. The ion density decreased to 2.0 × 1018m-3 with increasing distance from 50 to 150mm. The ion density changed with the energy inputted into the plasma.