An endoscope insertion portion includes an image pick-up assembly including an image pick-up unit and an image pick-up cable provided in order from the distal end portion to the proximal end side wherein the outer diameter of the image pick-up unit is larger than the outer diameter of the image pick-up cable, and a channel assembly arranged side by side with the image pick-up assembly and including a thin outer diameter portion and a thick outer diameter portion provided in order from the distal end portion to the proximal end side wherein a distal end portion of the thick outer diameter portion is arranged on more proximal end side than a proximal end portion of the image pick-up unit.
