To provide a private branch exchange system in which data is copied mutually between extension terminals without operating a main control device of a private branch exchange.

A private branch exchange system comprises a digital line circuit DL1 including a terminal interface package 6a which performs sequence control for transferring data of a telephone directory or the like stored in a digital multi-functional telephone set TEL1a or a digital multi-functional telephone set TEL1b, to the digital multi-functional telephone set TEL1b or the digital multi-functional telephone set TEL1a, and storing the data.