A body fluid collection device comprises a longitudinal member having a lumen formed along a longitudinal axis and configured to be inserted through the channel, a flow path in which a suction is acted by the suction section of the endoscope, which is formed to bring the lumen of the longitudinal member in communication with the channel, an accommodating section which is formed in the flow path, and accumulate the the body fluid suctioned in the lumen by the suction section of the endoscope, and a sealing member configured to seal a space between the longitudinal member and the channel closer to a distal end of the longitudinal member than the suction port so that a fluid does not flow from the distal end side to a proximal end side of the longitudinal member.