An endoscope system includes a mother endoscope, a baby endoscope and a fixing member. The mother endoscope includes a first insertion section, a first operation section, a treatment instrument insertion channel and an opening. The baby endoscope includes a second insertion section and a second operation section. The first operation section includes a projection portion. The second operation section includes a recess portion that is a recessed face formed such that at least part of the recessed face comes into face contact with a surface of the projection portion. The second operation section is fixed to the first operation section in a state where the recess portion is in contact with the surface of the projection portion.