A washing and rinsing method in a washer is disclosed, by which a washing power is raised by rotating a drum irregularly to enable a laundry and water to move in a disordered pattern. The present invention includes a referential rotational speed setting step of setting a referential rotational speed of a drum having a laundry accommodated therein to perform a washing or rinsing on the laundry, an actual rotational speed setting step of setting an actual rotational speed within a range having a prescribed variation from the referential rotational speed set by the referential rotational speed setting step, and a drum rotating step of rotating the drum according to the actual rotational speed if the actual rotational speed is set by the actual rotational speed setting step.