A signal processing circuit for a rotation detector includes a normal-rotation pulse request holding portion, a reverse-rotation pulse request holding portion, a resetting portion, and a waiting time switching portion. When an output of one of a normal-rotation pulse and a reverse-rotation pulse is finished and a waiting time elapses, the resetting portion resets an output request signal of the one of the normal-rotation pulse and the reverse-rotation pulse held by one of the pulse request holding portions. The waiting time switching portion sets the waiting time to a first waiting time when one of the pulse request holding portions holds the output request signal, and the waiting time switching portion sets the waiting time to a second waiting time longer than the first waiting time when both the pulse request holding portions hold the output request signals.