Blood collecting apparatus and blood collecting method using blood collecting apparatus

A blood collecting apparatus comprises a blood collecting needle ; the blood collecting bag, a first tube whose one end communicates with the blood collecting bag and other end communicates with the blood collecting needle, the branch portion provided on a portion of the first tube, a second tube connected with the branch portion at one end thereof and having a blood take-out port (sampling port); and a flexible resin bag including a third tube communicating with the second tube. The flexible resin bag is capable of accommodating air inside a part of the first tube between the branch portion and the blood collecting needle and air inside the second tube when the blood collecting apparatus is used.