A treatment instrument insertion assisting tool 10 for assisting insertion of a treatment instrument into a body is capable of inserting a treatment instrument inside and includes an inner tube 20 having flexibility, an inner tube 20 insertable inside And an outer tube 30 having flexibility. Both end portions 20B of the inner tube 20 are made of a hard material, and the intermediate portion 20A between the both end portions 20B is made of a soft material.
