An imaging device includes: an imaging element that generates an image signal of a subject; an observation method determining unit that determines, based on identification information indicating types of a control device connected to the imaging device, whether the control device adopts a first observation method for processing an image signal indicating a plurality of images of the subject per one frame period or a second observation method for processing an image signal indicating a single image of the subject per one frame period; and a data reducing unit. If the control device adopts the second observation method, the data reducing unit reduces a data amount of the image signal to be transmitted to the control device per unit time such that a transmission rate indicating the data amount of the image signal per unit time is acceptable to the control device that adopts the second observation method.