Disclosed is a disposable blood collecting instrument that stably secures a sufficient volume of blood with a single puncture. A tip portion of a piercing body of a lancet contained within a housing projects by means of a biasing force of a spring assembly, and a surrounding area of an opening of the housing is made a transparent visible portion with a visible interior. Additionally, the disposable blood collecting instrument has been formed such that the spring assembly is contained within housing farther behind the piercing body than a position of the tip portion of the piercing body that has entered within the housing after piercing.
