An object is to directly detect the emptiness of a solvent cartridge being mounted. An emptiness detection unit body includes a light transmissive tube which constitutes part of internal piping of a printer body, a light emitter, and a light receiver. The light transmissive tube is composed of a transparent tube, typically, a glass tube or a fluororesin (PFA) tube. The light emitter and the light receiver are arranged to face the light transmissive tube. The light transmissive tube is filled with a solvent supplied from the solvent cartridge. On the other hand, the light transmissive tube is filled with gas when the solvent cartridge is empty. The emptiness of the solvent cartridge is detected by a change in the amount of light received by the light receiver associated with the change in the light transmissive tube.