PURPOSE: To quickly transfer packet data by assigning plural time slot groups, each of which consists of a certain number of time slots, to line circuit groups for packet switching.

CONSTITUTION: Plural line circuits PLC are divided into Knumber of line circuit groups, and N-number of time slot groups each of which consists of M-number of time slots are provided in a data frame on a common data bus. Each line circuit PLC is connected to two control busses C1 and C2 connected to an arbiter circuit 2. In this constitution, each line circuit PLC uses one bit of the assigned time slot of the control bus to request the use of the time slot group, and the arbiter circuit 2 checks whether collision occurs or not only in the line circuit group, to which this line circuit belongs, and uses one bit of the time slot of the control bus to return the use permission of the time slot group whose use right the line circuit group has.