A dialysate extraction device comprising: a dialysate extraction means including an inlet port and an outlet port adapted to be connected to a flow path of fluid for flowing the fluid therethrough and a projected collection port having a circular cross-section for collecting the fluid flowing through the inlet and outlet port (9a, 9b); a outer circumference wall part mounted on the dialysate extraction means so that it covers a projected end of the collection port and is projected therefrom; a connection member (15, 17) formed with a connection portion (15aa, 17aa) to be connected to the collection port and a fitting portion (16, 17d) to be fitted into an inner circumference of the outer circumference wall part and adapted to extract the fluid through the collection port under a condition in which the connection portion (15aa, 17aa) is connected to the outer circumference wall part; and correction portions (13d, 13e) formed on the inner circumference of the outer circumference wall part for correcting position and attitude of the connection member (15, 17) relative to the collection port before a tip end (15c, 17c) of the connection member (15, 17) reaches the projected end of the collection port during insertion of the connection member (15, 17) into the outer circumference wall part; wherein a length (La) between the projected end of the collection port and a tip end of the outer circumference wall part is substantially same as or larger than a length (Lb, Lc) between the tip end (15c, 17c) of the connection member (15, 17) and the fitting portion (16, 17d) of the connection member (15, 17); and wherein an outer diameter D3 of the fitting portion or an outer diameter D2 of a seal member as the fitting portion, respectively, is the same as or slightly larger than an inner diameter D1 of the outer circumference wall part. a dialysate extraction means including an inlet port and an outlet port adapted to be connected to a flow path of fluid for flowing the fluid therethrough and a projected collection port having a circular cross-section for collecting the fluid flowing through the inlet and outlet port (9a, 9b); a outer circumference wall part mounted on the dialysate extraction means so that it covers a projected end of the collection port and is projected therefrom; a connection member (15, 17) formed with a connection portion (15aa, 17aa) to be connected to the collection port and a fitting portion (16, 17d) to be fitted into an inner circumference of the outer circumference wall part and adapted to extract the fluid through the collection port under a condition in which the connection portion (15aa, 17aa) is connected to the outer circumference wall part; and correction portions (13d, 13e) formed on the inner circumference of the outer circumference wall part for correcting position and attitude of the connection member (15, 17) relative to the collection port before a tip end (15c, 17c) of the connection member (15, 17) reaches the projected end of the collection port during insertion of the connection member (15, 17) into the outer circumference wall part; wherein a length (La) between the projected end of the collection port and a tip end of the outer circumference wall part is substantially same as or larger than a length (Lb, Lc) between the tip end (15c, 17c) of the connection member (15, 17) and the fitting portion (16, 17d) of the connection member (15, 17); and wherein an outer diameter D3 of the fitting portion or an outer diameter D2 of a seal member as the fitting portion, respectively, is the same as or slightly larger than an inner diameter D1 of the outer circumference wall part.