Disclosed herein is 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. The guidewire inserter is a tubular member having therein a bore for passage of a guidewire. The tubular member has a slit cutting across the wall thereof over the total length thereof. The tubular member has at the proximal end thereof an aperture, which results from the slit expanding toward the proximal end. The tubular member has at the proximal end of the aperture an open part and a connecting part adjacent thereto for the holder tube. There are 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 with respect to the central axis of the tubular member. When the distal end of the tubular member is connected by insertion into the bore at the proximal end of the tube, such as sheath, the protruded rims come into contact with the inside of the hub.