To prevent a reduction in the performance of a unit cell due to a gas shortage in a cathode chamber. An electrochemical reaction unit includes a unit cell, a cathode-side member, and an anode-side member. The electrochemical reaction unit satisfies the following condition on at least one of supply and discharge sides of the cathode chamber. Condition: the distance between the midpoint between opposite end points of a cathode-side opening group including an opening of a cathode-side communication channel and the midpoint (specific point) between opposite end points of an anode-side supply opening group including an opening of an anode-side supply communication channel in a direction parallel to an inner circumferential surface of a cathode chamber hole is shorter than the distance between the centroid of a cathode-side gas channel hole and the specific point in the direction parallel to the inner circumferential surface of the cathode chamber hole.