PURPOSE: To improve the using efficiency of a bus by generating a bus use permission signal corresponding to the bus use requesting quantity of each data transfer device.

CONSTITUTION: A bus control device 1 permitting the use of a data bus to each data transfer device is provided with a priority order storing table 1114 storing plural priority order sorts corresponding to the data transfer devices, a counter 112 formed correspondingly to each corresponding data transfer device, an adder 1111 corresponding to each data transfer device to add '1' to the counter 1112 when a data transfer request is generated from the corresponding data transfer device, an address generating circuit 1113 for selecting one of the priority sorts from the table 1114 while referring the value of the counter 1112, a selecting circuit 12 for selecting a data transfer device in accordance with the priority order selected by the circuit 1113, a subtractor 1115 for subtracting '1' from the counter 1112 corresponding to the data transfer device selected by the circuit 12, and a bus use permission signal generating circuit 13 for permitting the use of the data bus 3 to the data transfer device selected by the circuit 12.