Silver electrical contacts are separated at constant speed and break arcs are generated in a DC100V-450V/10A resistive circuit. The transverse magnetic field of a permanent magnet is applied to the break arcs. Dependences of the arc duration, arc dwell time and arc lengthening time on the strength of the magnetic field and supply voltage are investigated. The characteristics of the re-ignition of the break arc are also discussed. Following results are shown. The arc duration D is increased due to the increase of the arc lengthening time t_m when the supply voltage E is increased for each magnetic flux density B_x, because the arc dwell time t_s is almost constant. The arc duration D is increased due to the increase of both of the arc lengthening time t_m and the arc dwell time t_s when the magnetic flux density B_x is decreased. The arc lengthening time tended to become long when the re-ignition of the break arc is occurred. The lengthening time tends to become longer when the duration t_m1 from the start of the arc lengthening to the start of the re-ignition is increased. Re-ignitions occurred frequently when the magnetic flux density of the transverse magnetic field is increased and the supply voltage is increased.