An automatic operating apparatus for magnetic recording and reproducing apparatus in which there is provided a cam integrally revolving by revolution of an operating knob, means for engaging a pinch roller cooperating with a capstan and an idler cooperating with a reel disk in a waiting position in association with the revolution of the cam, and means for releasing the pinch roller and idler from the waiting position by closing of a timer switch at a pre-set time thus starting an automatic recording or reproducing operation. There is further provided means for detecting the presence or absence of a magnetic tape and means for returning the cam to the stop position thereby stopping the recording or reproducing operation.