In an endoscope system including an endoscope having an insertion section and an operation section and a disposable protection cover having an insertion section cover having formed therein a forceps channel and a forceps inlet opening through which a forceps can be inserted into the forceps channel, the forceps inlet opening is selectively closed by a forceps plug which is made of resilient material and separately formed from the insertion section cover. The forceps plug is preferably formed such that it can be detachably secured to a forceps inlet opening of an ordinary coverless (without-cover} endoscope.