An endoscope is characterized by including a distal end forming portion (12) forming a distal end portion of the endoscope and extending in an axial direction, an image pick-up unit (32) extending in the axial direction within the distal end forming portion (12), a channel tube (44) extending in the axial direction within the distal end forming portion (12) and including a parallel portion (46) arranged parallel with the image pick-up unit (32), and wherein the parallel portion (46) includes an inner peripheral surface and an outer peripheral surface, and the outer peripheral surface includes a facing side diameter reducing portion (58a 62 64a 70a) arranged on a side facing the image pick-up unit (32) and, with respect to a reference circumferential surface (P) including a common central axis to the inner peripheral surface, closer to a central axis side than the reference circumferential surface (P) in a cross section orthogonal to the axial direction, and a diameter keeping portion (60 66 68) arranged on a side other than the side facing the image pick-up unit (32) and whose at least a part overlaps the reference circumferential surface (P).
