Droplet ejection apparatus

A droplet ejection apparatus which includes: a platen on which an ejection target medium is conveyed; a head that ejects droplets toward the platen, the head being provided in a reciprocable manner along the platen; a light emitting device that emits a light in an oblique direction toward the platen within a plane including a straight line along a moving direction of the head and a normal line with respect to the platen; a light receiving device that receives the light emitted from the light emitting device and regularly reflected by one of the platen and the ejection target medium; and a calculation device that calculates a distance between the one of the platen and the ejection target medium, and the head, based on a position at which the light receiving device receives the light during a movement of the head. One of the light emitting device and the light receiving device reciprocably moves integrally with the head, and the other is provided separately from the head.