PROBLEM TO BE SOLVED: To provide an air trap chamber capable of more sufficiently and reliably removing air bubbles included in a predetermined liquid, and also capable of reducing the volume of a chamber part.SOLUTION: Provided is an air trap chamber 5 that comprises: a chamber part 5c connected to a blood-circulating blood circuit and capable of receiving a predetermined volume of blood a blood introduction inlet 5aa capable of introducing blood in the blood circuit into the chamber part 5c and a blood discharge outlet 5ca capable of discharging the blood in the chamber part 5c to the blood circuit, and that traps and removes air bubbles included in the blood received in the chamber part 5c, the air trap chamber 5 being characterized in comprising a wall part 7 capable of causing the blood introduced through the blood introduction inlet 5aa to flow upward, and then causing the blood to flow downward toward the chamber part 5c.SELECTED DRAWING: Figure 3
