PURPOSE: To improve the utilizing effect by designing the device that a line during incoming or retention is brought into a tentative reserved state when plural telephone sets make reservation operation to the line to attain instantly the response from other telephone sets freely even if a telephone set having no will of response makes a resevation operation.
CONSTITUTION: When a hook switch HS of telephone sets STa, STb is turned on by off-hook, truck lines CO1, CO2 are selected by main wire buttons SWc1, SWc2 and a retention button SWh is operated, then a holding circuit HLD is activated to control a connecting section CN thereby holding the main wires CO1, CO2. On the other hand, when the incoming information of the main wires CO1, CO2 is given to a memory MEM and the main wire button corresponding to the main wire during incoming in the telephone sets STa, STb is operated while being hooked off, the storage of the tentative reserved registration is attained by a memory MEM for the telephone sets STa, STb.
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