Provided are an image sensor, an imaging device, an endoscope, and an endoscopic system which are capable of eliminating an in-phase fluctuation component of a power supply superimposed on an image signal. A first chip 21 includes: a light receiving unit 23 that has a plurality of photoelectric conversion elements, which are arranged in a two-dimensional matrix form and each of which receives light from outside and accumulates a charge according to the amount of received light an imaging signal generating unit 240 which converts the charge accumulated in each of the plurality of photoelectric conversion elements into a voltage and generates an imaging signal, and a reference signal generating unit 248 which generates a reference signal having a fluctuation component with the same phase as the imaging signal generated by the imaging signal generating unit 240.
