An electrochemical reaction device comprising: an anode part configured to oxidize water and thus produce oxygen; a cathode part configured to reduce carbon dioxide and thus produce a carbon compound and hydrogen; a separator separating the anode part and the cathode part; and a power supply connected to the anode part and the cathode part, wherein the cathode part comprises: a conductor having a conductive surface; a gas diffusion porous body including a first surface, a second surface, a first porous portion, and a second porous portion, the first surface being in contact with the conductive surface, the first porous portion being in contact with at least one of the first surface or the second surface, the second porous portion being in contact with at least one of the first surface or the second surface, and a contact angle between an inner wall of the second porous portion and the water being higher than a contact angle between an inner wall of the first porous portion and the water; a reduction catalyst supported on the second surface to reduce carbon dioxide; an electrolytic solution flow path facing the reduction catalyst and configured to make an electrolytic solution containing the water flow; a first flow path facing the first porous portion and configured to discharge at least one of the water or water vapor from the first porous portion to an outside of the cathode part; and a second flow path facing the second porous portion and configured to make the carbon dioxide flow in the second porous portion from the outside of the cathode part and make at least one of the carbon compound or the hydrogen flow out to the outside of the cathode part from the second porous portion. an anode part configured to oxidize water and thus produce oxygen; a cathode part configured to reduce carbon dioxide and thus produce a carbon compound and hydrogen; a separator separating the anode part and the cathode part; and a power supply connected to the anode part and the cathode part, wherein the cathode part comprises: a conductor having a conductive surface; a gas diffusion porous body including a first surface, a second surface, a first porous portion, and a second porous portion, the first surface being in contact with the conductive surface, the first porous portion being in contact with at least one of the first surface or the second surface, the second porous portion being in contact with at least one of the first surface or the second surface, and a contact angle between an inner wall of the second porous portion and the water being higher than a contact angle between an inner wall of the first porous portion and the water; a reduction catalyst supported on the second surface to reduce carbon dioxide; an electrolytic solution flow path facing the reduction catalyst and configured to make an electrolytic solution containing the water flow; a first flow path facing the first porous portion and configured to discharge at least one of the water or water vapor from the first porous portion to an outside of the cathode part; and a second flow path facing the second porous portion and configured to make the carbon dioxide flow in the second porous portion from the outside of the cathode part and make at least one of the carbon compound or the hydrogen flow out to the outside of the cathode part from the second porous portion. a conductor having a conductive surface; a gas diffusion porous body including a first surface, a second surface, a first porous portion, and a second porous portion, the first surface being in contact with the conductive surface, the first porous portion being in contact with at least one of the first surface or the second surface, the second porous portion being in contact with at least one of the first surface or the second surface, and a contact angle between an inner wall of the second porous portion and the water being higher than a contact angle between an inner wall of the first porous portion and the water; a reduction catalyst supported on the second surface to reduce carbon dioxide; an electrolytic solution flow path facing the reduction catalyst and configured to make an electrolytic solution containing the water flow; a first flow path facing the first porous portion and configured to discharge at least one of the water or water vapor from the first porous portion to an outside of the cathode part; and a second flow path facing the second porous portion and configured to make the carbon dioxide flow in the second porous portion from the outside of the cathode part and make at least one of the carbon compound or the hydrogen flow out to the outside of the cathode part from the second porous portion.