A dial device for a telephone set having a function of preventing toll dialing, in which a resistor or a zener diode is connected in series to a dial impulse contact of the dial device while a series connection of a first diode and a control circuit is connected in parallel with the resistor or the zener diode. A series-connection of a minimum pause contact and a second diode is connected in parallel with the dial impulse contact. An AND output of a dial impulse signal and a minimum pause signal from the minimum pause contact is obtained from a junction between the dial impulse contact and the first diode to apply it to a first input terminal of the control circuit, while the minimum pause signal is obtained from a junction between the minimum pause contact and the second diode to apply it to a second input terminal of the control circuit. A semiconductor switching element is connected in shunt with the dial impulse contact to prevent the sending-out of dialled impulses in response to the output of the control circuit when the dial impulse signal is a series of numbers representative of the toll dialling starting from a number 0 or numbers 10.