An endoscope system, including an endoscope and first and second connectors (60, 75, 85, 105), said endoscope having an elongated tube for entry in a body cavity for imaging, a fluid channel, formed inside said elongated tube, for transferring fluid, and a port device (42, 71, 81, 101), disposed on a proximal end side of said elongated tube, for communicating with said fluid channel, said first and second connectors being configured to be selectively coupled with said port device, wherein: said port device includes: a sleeve portion having an opening (43, 72, 82, 102); a flange (42a, 71a, 81a, 101a) formed to project radially from an outer surface of said sleeve portion; a first tapered portion (43a, 72a, 82a, 102a) formed in said opening; said first connector includes: a flow sleeve for entry in said opening; a sealing structure for sealing an outer surface of said flow sleeve entered in said opening; an engaging device for engagement with said flange; said second connector (60, 75, 85, 105) includes: a coupling sleeve (62, 114) for entry in said opening; a second tapered portion, formed with said coupling sleeve, and tapered in compliance with said first tapered portion; a fastening device (66, 79, 86, 106) for fastening with said port device; a pusher (66, 79, 87) for pressing said second tapered portion to said first tapered portion upon fastening of said fastening device with said port device, to seal said first and second tapered portions. said port device includes: a sleeve portion having an opening (43, 72, 82, 102); a flange (42a, 71a, 81a, 101a) formed to project radially from an outer surface of said sleeve portion; a first tapered portion (43a, 72a, 82a, 102a) formed in said opening; a sleeve portion having an opening (43, 72, 82, 102); a flange (42a, 71a, 81a, 101a) formed to project radially from an outer surface of said sleeve portion; a first tapered portion (43a, 72a, 82a, 102a) formed in said opening; said first connector includes: a flow sleeve for entry in said opening; a sealing structure for sealing an outer surface of said flow sleeve entered in said opening; an engaging device for engagement with said flange; a flow sleeve for entry in said opening; a sealing structure for sealing an outer surface of said flow sleeve entered in said opening; an engaging device for engagement with said flange; said second connector (60, 75, 85, 105) includes: a coupling sleeve (62, 114) for entry in said opening; a second tapered portion, formed with said coupling sleeve, and tapered in compliance with said first tapered portion; a fastening device (66, 79, 86, 106) for fastening with said port device; a pusher (66, 79, 87) for pressing said second tapered portion to said first tapered portion upon fastening of said fastening device with said port device, to seal said first and second tapered portions. a coupling sleeve (62, 114) for entry in said opening; a second tapered portion, formed with said coupling sleeve, and tapered in compliance with said first tapered portion; a fastening device (66, 79, 86, 106) for fastening with said port device; a pusher (66, 79, 87) for pressing said second tapered portion to said first tapered portion upon fastening of said fastening device with said port device, to seal said first and second tapered portions.