A voltage-current converting converts a voltage signal into a current signal. In an example operation, a source of a transistor is connected to a first power source, the source is connected to an input terminal via a coupling capacitor, and a gate and a drain of the transistor are connected to a second power source so that current flows between the source and the drain while a constant voltage is applied to the input terminal. To output the current signal, the drain is disconnected from the second power source, the voltage signal is supplied from the input terminal to the holding capacitor via the coupling capacitor, the coupling capacitor is disconnected from the input terminal, the gate is disconnected from the second power source, the drain is connected to the second power source, and the source is connected to an output terminal.