PURPOSE: To inform the operator of operation produedures with voice when he wants to confirm them, by storing operation procedures of a key telephone in a memory.

CONSTITUTION: If the operator acquires an extension trunk and depresses button keys "*" and "1" when he wants to confirm the operation method of an extension telephone set TEL1, this information is sent to a data interface DI in a main equipment. A central processing device CPU controls a channel switch SW to connect a voice synthesizing circuit VS to the telephone set TEL1. Meanwhile, the voice synthesizing circuit VS synthesizes a voice for the inquired operation method and sends it to the telephone set TEL1 through the channel switch SW, a voice interface LI, and a voice bus 11. The operation method is annuounced through the handset or an incorporated speaker in the telephone set TEL1.