The invention relates to a field-effect transistor, a display element, an image display device, and a system. The field-effect transistor includes: a base; a passivation layer; a gate insulating layerformed therebetween; a source electrode and a drain electrode, which are formed to be in contact with the gate insulating layer; a semiconductor layer, which is formed between at least the source electrode and the drain electrode, and is in contact with the gate insulating layer, the source electrode, and the drain electrode; and a gate electrode, which is in contact with the gate insulating layer, and faces the semiconductor layer via the gate insulating layer, wherein the passivation layer contains a first passivation layer, which contains a first composite metal oxide containing Si, and analkaline earth metal, and a second passivation layer, which is formed to be in contact with the first passivation layer, and contains a second composite metal oxide containing an alkaline earth metal, and a rare-earth element.