A position measuring device comprising includes an imager, and at least one processor configured to execute a program stored in a memory. The at least one processor detects, from an imaging range of a picture image acquired by the imager, a light-emitter image of a first light emitter that is capable of movement in a space and emits light corresponding to identification information of the first light emitter in the space, and acquires a three-dimensional position of the first light emitter in the space based on a position of the detected light-emitter image of the first light emitter in the picture image.