A needle threader includes a needle bar supporter to which a needle bar holding a needle with a needle hole is attached, a threader shaft supported in a movable manner in a vertical direction and in a rotatable manner, a thread holding mechanism which is held by the threader shaft and which applies a tension to a thread so as to be substantially horizontal ahead of the needle hole, and a threader mechanism which is held by the threader shaft and which comprises a threader hook that enters the needle hole upon a rotation of the threader shaft. The threader hook includes a capturing portion that captures the thread at a tip part of the capturing portion. The capturing portion includes a thread pathway where the thread enters or leaves, and a thread capturing space for capturing the thread. A width of a part where the thread pathway becomes the narrowest is formed so as to be narrower than a width of the thread capturing space. The thread enters or leaves the thread pathway in a tensioned condition, and the width of the part where the thread pathway becomes the narrowest is formed so as to be narrower than an outer diameter of the thread not in a tensioned condition.