A circuit for preventing impulse generation caused by operating a hook switch in a telephone set, in which the hook switch has a make contact and a break contact which are make-before-break contacts in going to the OFF-hook condition, and are break-after-make contacts in going to the ON-hook condition. A capacitor is charged through the make contact when it is closed in the OFF-hook condition. A transistor switching circuit is provided to turn ON by the charge on the capacitor so as to short-circuit between telephone line terminals of the telephone set when the break contact is closed in the ON-hook condition.