a magnetic a tape recording / reproducing apparatus comprises a tape running unit , a recording and reproducing unit , a data memory , and a controller . the controller controls the tape running unit , the data memory and the recording and reproducing unit such that , in a recording mode , the input data are continuously written into the data memory at a first a data rate and the written data are intermittently read out from the data memory at a second data rate which is higher than the first data rate and intermittently recorded onto a magnetic tape , and that , in a reproduction mode , the recorded data are intermittently reproduced from the magnetic tape and intermittently written into the data memory at the second data rate and the written data are continuously read out from the data memory at the first data rate . the controller is responsive to indication information indicating that the tape is not in a recordable or reproducible position for stopping reading operation in the recording mode and writing operation in reproduction mode of the data memory and operation of the recording and reproducing unit and for controlling the tape running unit to transfer the tape to a recordable or reproducible position .