A blood collecting device collects blood in a short time after puncture without scattering the blood into the open air other than a container for collecting the blood. One of representative blood collecting devices has a container unit that includes a screw portion, a holder that holds the container unit serving as a system whose one end is closed, a puncture unit that can be attached to the container or the holder, a through-hole of the puncture unit, and a puncture unit protection member that protects the puncture unit and the container unit.