A life detection device of an encoder is used for the encoder including a scale and a head. The scale is housed in a scale frame. The head relatively moves along the scale to detect an amount of relative movement with the scale. The life detection device includes environmental condition detection means, life determination means, and informing means. The environmental condition detection means is configured to detect an environmental condition related to life detection in the encoder. The life determination means is configured to determine a life of a component constituting the encoder based on a detection result by the environmental condition detection means. The informing means is configured to inform the life based on a determination result by the life determination means.