A treatment system includes a guide, tubular dilator members, an operation portion, and a holding portion. The guide extends linearly or curvilinearly. The dilator members pass the guide inside and are configured to move forward along the guide. The operation portion is configured to sequentially move the plurality of dilator members from a proximal end side of the guide to a distal end side of the guide. The holding portion is provided on the guide. A distance between outer edges of the holding portion in a direction intersecting a direction from the proximal end side toward the distal end side of the guide is larger or is configured to be larger than a distance between outer edges of the guide.
