An linear encoder includes: a scale; a light-emitting element that emits light onto the scale; a detecting head that has a light-receiving element that receives the light emitted by the light-emitting element to be reflected or transmitted by the scale; and a connector connected to the detecting head via a cable. The connector comprises a display that displays a status of the light received by the light-receiving element and a connector controller that controls the display. The connector controller includes a display controller that controls the display in accordance with the intensity of the light received by the light-receiving element.