PURPOSE: To omit the confirmation of presence and absence of a called telephone reservation destination by storing the information of a caller extension to an area of a called telephone set of a reservation memory and calling the caller extension when the talking of the called telephone set is terminated to connect the caller to the called telephone set.

CONSTITUTION: When an extension telephone set 1 makes a call but an extension telephone set 3 does not reply the call, the user of the extension telephone set 1 hooks on its handset and dials a reservation special number. A central controller 4 uses the special number to access a reservation memory 5 and the information of the extension telephone set 1 being a reservation destination is stored in a location accommodation corresponding area of the extension telephone set 3. When the user of the extension telephone set 3 comes back, makes a call to somewhere and its talking is finished, the central controller 4 accesses the reservation memory 5 to read the reservation information from the area corresponding to the accommodated location of the extension telephone set 3 in the reservation memory 5 to call the extension telephone set 1. Thus, the conformation of the presence of the reservation opposite destination is omitted in this way.