An endoscope system which an insertion portion (10) is inserted from an insertion opening (I) of an object (O) to observe an inner surface of the object includes an illumination unit (12) which includes a modulation section (14) that controls a visible light source so that visible light from the visible light source is subjected to intensity modulation in a predetermined pattern, and which emits modulated visible light as illumination light, a detection section (16) which detects the modulated visible light, and a determination section (18) which determines whether the insertion portion (10) is present in the object based on a detection result of the detection section (16). The illumination unit (12) is arranged outside the object, and the detection section (16) is arranged at the insertion portion (10).
