PURPOSE: To apply an economical route selection (LCR) even in the digital communication mode or the like except the talking mode by deciding whether or not the LCR is to be applied in response to the transmission capability of a call when a PABX accommodating an ISDN line acquires an ISDN line and makes a call.

CONSTITUTION: At first a transfer capability is defined for line setting of an extension terminal equipment such as an extension telephone set 22 and a data terminal equipment 23 in a PABX 21 and a discrimination circuit data representing whether or not the LCR is to be applied based on the transfer capability is stored in a memory 30 of the PABX 21. When the PABX 21 receives a dial signal to acquire an ISDN line 24 from an extension terminal equipment such as an extension telephone set 22 and a data terminal equipment 23, the discrimination whether or not the LCR is to be applied as the system in the PABX 21 is implemented by using a discrimination data stored in the memory 30 in the PABX 21. Thus, the LCR is automatically applied even in the digital communication mode except the talking mode.