To provide a fuel cell stack for being operated with a cooling water flow in a wide range by suppressing entrance of air bubbles and screening them out during an operation for cooling latent heat down.

The fuel cell stack is formed by alternately laminating unit cells 1 and fuel cell separators 2 each of which includes a cooling water passage portion 8. A first cooling water passage 22 formed in the cooling water passage portion 8 is divided into a plurality of sections 31, 32, 33 and 34, and, in the sections 31, 32, 33 and 34, a plurality of first grooves 21 are arranged at regular intervals so as to flow cooling water in the first grooves 21. Further, the fuel cell stack includes second cooling water passages 23 and 24 constituted so as to be coupled with the first cooling water passage 22 by passing cooling water in the grooves extending in a direction perpendicular to the first grooves 21 and formed in each of both end portions of the first grooves 21, and third cooling water passages 25 and 26 constituted so as to flow cooling water by coupling the second cooling water passages 23 and 24, and a cooling water supply portion 15 or a cooling water drainage portion 16.