The invention aims at providing a measurement support device, an endoscope system, and a processor for an endoscope system capable of displaying an accurate indicator with a simple configuration. In a measurement support device related to one aspect of the invention, the coordinates of a spot, and coordinates of points indicating an actual size of a measurement target in a subject and indicating a circular marker distorted in accordance with distortion aberration of an imaging optical system are stored in association with each other in a storage unit, the coordinates of the points indicating the circular marker are acquired with reference to the storage unit on the basis of the measured coordinates of the spot, and the circular marker is displayed on the basis of the acquired coordinates. Thus, the distance measurement is unnecessary, the configuration is simple, and the processing load is low. Additionally, since the circular marker is displayed in the vicinity of the spot (for example, centering on a spot position), there is little deviation between the spot position and a marker position, the circular marker is accurate as an indicator. Additionally, since the indicator is not widely displayed, there is little processing load.