Check valve and refrigeration cycle system

The utility model provides a check valve capable of preventing fluid leakage during valve closing and a refrigeration cycle system. A valve body (4) of the check valve is provided with a valve body component (41) and a valve seat component (42) capable of being seated on a valve seat part, and the valve body component (41) is provided with a clamping hole (411) used for fixing the valve seat component (42) to the valve body component (41). The valve seat member (42) is provided with: a valve seat main body (421) capable of coming into contact with the valve seat part; and an engagement section (422) which is integrally formed on a surface (421b) of the valve seat body (421) on the opposite side from the valve seat section, protrudes from the surface (421b) on the opposite side toward the valve body member (41), can engage with the engagement hole (411), and fixes the valve seat member (42) to the valve body member (41) by the engagement of the engagement section (422) into the engagement hole (411). 本实用新型提供一种