Disclosed is a disposable blood collecting instrument that stably secures a sufficient volume of blood with a single puncture. The tip (63) of a piercing body (62) on a lancet (11) contained within a housing (10) projects by means of the impelling force of a spring member (12), and the section surrounding the opening (38) of the housing (10) is made a transparent visible section (59) with a visible interior. Additionally, the disposable blood collecting instrument has been formed such that the spring member (12) is contained within housing farther behind the piercing body (62) than the position of the tip (63) of the piercing body (62) that has entered within the housing (10) after piercing.
