A sheet transport switching device include a rotary guide that is pivotal about an axis orthogonal to a sheet transport direction to align a guide passage with one of two discharge destinations. A stepping motor changes the posture of the rotary guide and a controller controls the stepping motor. A lead end in-timing acquirer acquires a timing when a lead end of the sheet enters the guide passage. The controller performs, in a state that the exit of the guide passage aligns with one of the two discharge destinations, an in-timing retaining operation of retaining a rotated position of the stepping motor by supplying an energizing current of a first current value to the stepping motor at the acquired lead end in-timing, and a pass timing retaining operation of reducing the energizing current to a second value when the lead end of the sheet passes the guide passage.