the present invention provides a magnetic recording and reproducing unit of a helical scan type having a slow speed tape running mode in which the speed of running a magnetic tape is slower than that of a standard running mode . the magnetic recording and reproducing unit of the present invention has a pair of azimuth heads of mutually different azimuthal angles which are mutually adjacently disposed on the outer periphery of a rotating cylinder and another pair of azimuth heads of mutually different azimuthal angles which are mutually adjacently disposed at positions symmetrical with the first pair of azimuth heads with respect to a rotating center of the rotating cylinder . each pair of the two pairs of azimuth heads alternately traces tracks recorded with image signals on a magnetic tape to reproduce the recorded image signals . further , the magnetic recording and reproducing unit of the present invention has a control head for reproducing from the magnetic tape a control signal which is synchronous with a header position of the recorded tracks , a traced azimuth predicting signal generating unit for generating a predetermined azimuth change over signal in response to the control signal , and a switching unit for selecting one of reproduced image signals from the pair of azimuth heads according to the change over signal in the slow speed running mode .