A telephone system, comprising telephone sets, exchange device and server device, wherein a telephone set has notification unit accepting log-in operation and server device includes user management table associating each telephone number of telephone sets with identification information of users, address management table dynamically associating each telephone number of users with address information, specification processor specifies telephone number of logged-in user when log-in operation is performed, verification processor verifies presence/absence of registration of specified telephone number, determination processor determines coincidence/discordance between address information and notified address information, and update processor updates address management table by overwriting address information, if the notified address information does not coincide with address information corresponding to registered telephone number.