A fuel cell stack, comprising: a stacked plurality of single cells, each of the single cells comprising a membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly therebetween, wherein a cooling fluid channel where a cooling fluid flows is formed between adjacent single cells, and the fuel cell stack further comprises a displacement absorbing member disposed in the cooling fluid channel to absorb a displacement between the single cells, wherein the displacement absorbing member comprises a channel flow resistance reducing means to reduce a channel flow resistance of the cooling fluid channel against the cooling fluid by preventing vortex flow of the cooling fluid, wherein the displacement absorbing member comprises a base plate and a number of spring functional parts arranged on one surface of the base plate, and the spring functional parts have a cantilever structure comprising a fixed proximal end fixed on the base plate and a free tip end, the displacement absorbing member being disposed so that the free tip end of spring functional parts faces toward a downstream of the flow direction of the cooling fluid, characterized in that the channel flow resistance reducing means is constituted by at least either an opening or a cutout (16, 36) formed in the spring functional parts between the free tip end and the fixed proximal end thereof, wherein the cutouts (16, 36) are formed by removing a part of the spring functional parts after forming them, or formed simultaneously with forming the spring functional parts by lancing the base plate, and wherein the displacement absorbing member comprises spring functional parts that have different shapes according to a location in the cooling fluid channel. a stacked plurality of single cells, each of the single cells comprising a membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly therebetween, wherein a cooling fluid channel where a cooling fluid flows is formed between adjacent single cells, and the fuel cell stack further comprises a displacement absorbing member disposed in the cooling fluid channel to absorb a displacement between the single cells, wherein the displacement absorbing member comprises a channel flow resistance reducing means to reduce a channel flow resistance of the cooling fluid channel against the cooling fluid by preventing vortex flow of the cooling fluid, wherein the displacement absorbing member comprises a base plate and a number of spring functional parts arranged on one surface of the base plate, and the spring functional parts have a cantilever structure comprising a fixed proximal end fixed on the base plate and a free tip end, the displacement absorbing member being disposed so that the free tip end of spring functional parts faces toward a downstream of the flow direction of the cooling fluid, characterized in that the channel flow resistance reducing means is constituted by at least either an opening or a cutout (16, 36) formed in the spring functional parts between the free tip end and the fixed proximal end thereof, wherein the cutouts (16, 36) are formed by removing a part of the spring functional parts after forming them, or formed simultaneously with forming the spring functional parts by lancing the base plate, and wherein the displacement absorbing member comprises spring functional parts that have different shapes according to a location in the cooling fluid channel.