A medical instrument with attached needle includes a needle tube (2) having a needle tip (2a) capable of piercing a living body and a needle holding member (5) for fixing and holding a middle portion of the needle tube (2) by high frequency welding so that the needle tip (2) protrudes from one end and a proximal portion (2b) of the needle tube (2) protrudes from the other end. It also has a seal member (8) composed of an elastic member and provided on an outer circumference of the proximal portion (2b) of the needle tube (2) so as to be liquid-tight, and a liquid containing member (9) having a liquid chamber capable of containing a liquid therein. With the proximal portion (2b) of the needle tube (2) communicating with the liquid chamber, the seal member (8) is compressed by and clamped between the needle holding member (5) and the liquid containing member (9).
