<p>It is possible to suppress destruction or degradation of a functional element which is attached or detached immediately after cutting off a drive power from a constant current power source or while the drive power is being supplied. Provided is an electric circuit including: a constant current power source (1) having an electrostatic capacitance between an output terminal and a reference potential terminal; and a functional element (2) which can be detachably attached. The electric circuit electrically connects the power source (1) to the functional element (2). The electric circuit includes an element destruction preventing circuit (10) having: a first circuit terminal connected to an output terminal of a constant current power source (1) via the functional element (2); and a second circuit terminal connected to the reference potential terminal of the constant current power source (1). The impedance between the circuit terminals is increased up to a non-connection mode impedance in accordance with transmission from the connection state when the functional element (2) is mounted, to the non-connection state when the functional element (2) is detached and the impedance between the circuit terminals is reduced down to the connection mode impedance in accordance with the connection state transition.</p>
