PURPOSE: To improve the service function of the exchanger at a hotel and the service to a guest room, by accesses CPU of the exchange priodically to the telephone set in the guest room and reading information, and changing the service class of the telephone set of the guest room according to the information.

CONSTITUTION: In a front key box FBK, a contact of a guest room key switch SW is contacted with the weight of the guest room key, the looping state generates detection information of the absence of key and information is delivered to a guest room key switch circuit KCT corresponding to a guest room automatic operation device CAS. The CPU of the exchanger accesses the telephone set a guest room and reads the information of use of guest room. As a result, the serv ice class of the guest room telephone set is changed according to absence/ presence information and stored in a memory. Thus, without almost changing the existing exchange function, the use of guest room can automatically be grasped.