A metal needle is obtained by being dipped in a liquid selected from the group consisting of a strong acid solution of a metal, acetic acid, and butyl acetate, and then dried. Preferably, the strong acid solution of a metal to be used in the dipping treatment may be a nitric acid solution of a metal selected from the group consisting of a transition element, a lanthanoid, and an actinoid, for example, a nitric acid solution of a metal selected from the group consisting of palladium, gadolinium, germanium, beryllium, strontium, scandium, and samarium. The metal needle is a metal needle for insertion into the body that can be reliably imaged even when a general-purpose ultrasound imaging system is used, and thus is useful in confirming insertion of the needle into a blood vessel and arrival of the needle at an organ, and confirming the position of the needle when it is broken.