1. An endoscope system for sequentially imaging plural predetermined examination parts of a patient and thereby acquiring still images of the respective examination parts by inserting an endoscope insertion unit having an imaging optical system in its tip portion into a body cavity of the patient, comprising: a number-of-images counting unit that counts the number of still images taken every time one of the predetermined examination parts is imaged; a number-of-images comparing unit that compares the counted number of still images with a preset number of images which corresponds to the number of the plural predetermined examination parts; an alert generating unit that generates an alert when the number-of-images comparing unit detects non-coincidence between the counted number of still images taken and the preset number; and an endoscope tip position detecting unit that detects a position, in the body cavity, of the tip portion of the endoscope insertion unit which is inserted in the body cavity.