An air trap chamber comprising: a chamber body that has a substantially cylindrical shape and has an upstream end defined with respect to a central axis (C1) and covered with a top wall having an inlet , and a downstream end defined with respect to the central axis and having an outlet ; and an inlet pipe that extends from the inlet into the chamber body , and has an ejection port , being an end opening, is provided at an inner circumference surface of the chamber body and faced in a circumferential direction, characterized in that the inner circumference surface of the chamber body extends, in a spiral shape in the circumferential direction, from an ejection point (P1) where the ejection port is located to a connection point (P2) where an outer circumferential surface of the inlet pipe surrounding the ejection port is coupled to the inner circumference surface of the chamber body , and a first distance (R1) connecting the ejection point (P1) and the central axis (C1) of the chamber body on a plane perpendicular to the central axis (C1) of the chamber body is longer than a second distance (R2) connecting the connection point (P2) and the central axis (C1) of the chamber body on the plane, wherein a connection point angle (θ) that is formed between a tangent line (L1) of the outer circumferential surface of the inlet pipe in a plane perpendicular to the central axis (C 1) and a tangent line (L2) of the inner circumference surface of the chamber body in a plane perpendicular to the central axis (C1) at the connection point (P2) and straddles the outer circumferential surface of the inlet pipe is 90° or less. a chamber body that has a substantially cylindrical shape and has an upstream end defined with respect to a central axis (C1) and covered with a top wall having an inlet , and a downstream end defined with respect to the central axis and having an outlet ; and an inlet pipe that extends from the inlet into the chamber body , and has an ejection port , being an end opening, is provided at an inner circumference surface of the chamber body and faced in a circumferential direction, characterized in that the inner circumference surface of the chamber body extends, in a spiral shape in the circumferential direction, from an ejection point (P1) where the ejection port is located to a connection point (P2) where an outer circumferential surface of the inlet pipe surrounding the ejection port is coupled to the inner circumference surface of the chamber body , and a first distance (R1) connecting the ejection point (P1) and the central axis (C1) of the chamber body on a plane perpendicular to the central axis (C1) of the chamber body is longer than a second distance (R2) connecting the connection point (P2) and the central axis (C1) of the chamber body on the plane, wherein a connection point angle (θ) that is formed between a tangent line (L1) of the outer circumferential surface of the inlet pipe in a plane perpendicular to the central axis (C 1) and a tangent line (L2) of the inner circumference surface of the chamber body in a plane perpendicular to the central axis (C1) at the connection point (P2) and straddles the outer circumferential surface of the inlet pipe is 90° or less. <EOS>