To provide a double seat valve that prevents first and second plugs from being inclined.

The double seat valve includes a pair of first and second valve seats 8, 9 provided on one axis, and a pair of first and second plugs 20, 21 which moves on axes of the first and second valve seats 8, 9 and simultaneously opens/closes the first and second valve seats 8, 9. An outlet-side space 10 between the first and second valve seats 8, 9 communicate with an outlet 2 through an outlet opening 11 with its one end opened only in one direction toward the outlet 2. The valve is also provided with a bulkhead cylinder 22 which separates the outlet-side space 10 between the first and second valve seats 8, 9 from the outlet opening 11. A plurality of communication holes 23 having a total opening area equal to an opening area of the first valve seat 8 is formed in the bulkhead cylinder 22. A plurality of communication holes 23, 24 are formed only on both sides in the direction perpendicular to the outlet opening 11.