According to one embodiment, a light-emitting device includes an emitting layer, first and second electrodes, a voltage-supply circuit, an ammeter and a controller. The emitting layer includes a solution containing an emitting material and a solvent. The first and second electrodes are in contact with the solution. The voltage-supply circuit applies an operating voltage between the first and second electrodes. The ammeter measures the amount of electric current flowing between the first and second electrodes. The controller controls the operation of the voltage-supply circuit such that the polarity of the operating voltage reverses and determining a timing of reversing the polarity based on the output of the ammeter.