PURPOSE: To reduce the time interval of a reading operation to a streamer type magnetic tape device SMTU by transferring the executing result including the remaining count value, etc., to a main memory MEM for each execution of the read instruction of a single block and therefore chaining many read instructions at one time.

CONSTITUTION: A magnetic tape controller MTC 1 stores the data transfer start address designated by a read instruction fetched from a MEM 3 to a bus controller together with the transfer byte number stored in a counter 40. Then the data on a single block read out of an SMTU 5 are continuously transferred to the MEM 3 via a buffer circuit 20 until no read data exists any more or the count value of the counter 40 is equal to zero. When the transfer of data is through, the addresses stored in an address counter 50 are transferred to the part 10 and the contents of the counter 40 storing the remaining count value are transferred to an address of the MEM 3. Thus the time interval can be reduced for a reading operation to an SMTU.