A device (such as guidewire inserter) for easily and certainly inserting a medical long item having a curved tip into a tube such as catheter and sheath includes a tubular member having a bore for passage of a guidewire. The tubular member has a slit cutting across the wall over the total length of the tubular member. The proximal end of the tubular member has an aperture. The proximal end of the aperture has an open part and a connecting part adjacent thereto for the holder tube. There is a pair of wing-like protruded pieces projecting in the mutually opposite directions at both sides of the open part. The distal end of the tubular member has on its outer surface a pair of protruded rims, which project in the mutually opposite directions.