A liquid ejecting apparatus includes a liquid ejecting head which ejects liquid toward a recording medium; a rib which projects in a direction toward the liquid ejecting head, and includes a support portion for supporting the recording medium; a detection target portion which is provided at a position lower than the support portion; a lower side portion located at a position lower than the detection target portion; a light emitting unit which irradiates the detection target portion with light rays; a light receiving unit which receives reflected light rays resulting from reflection of the light rays with which the detection target portion is irradiated, convers the received reflected light rays into photocurrent, and outputs the photocurrent as an output voltage; and a sensitivity setting unit which causes the light emitting unit to irradiate the detection target portion with light rays and sets the sensitivity of the light receiving unit.