NOVELTY - The structure (10) has a microporous layer (12) formed on a side of a diffusion layer (11) adjacent to a solid polymer electrolyte membrane (21) arranged between two electrodes in a membrane electrode assembly (MEA) (20) of a fuel cell i.e. solid polymer electrolyte fuel cell (1). The microporous layer contains carbon and a fluorocarbon resin, and has a water penetration pressure of about 5-180kilo Pascal. The structure satisfies a relation among an actual measurement value and a theoretical value of a pressure drop and a thickness, porosity and a mean flow pore size of the diffusion layer.    USE - Diffusion layer structure i.e. cathode-side structure, for a fuel cell i.e. solid polymer electrolyte fuel cell, utilized as a power source for an automobile.    ADVANTAGE - The structure limits a value obtaining by dividing the actual measurement value and the theoretical value to a range of 2-15 to obtain a low degree of sinuosity of pores and a low pressure drop across the diffusion layer so as to efficiently discharge water vapor produced in a cathode catalyst layer, thus increasing oxygen partial pressure in the vicinity of the cathode catalyst layer, and hence improving electric power generation performance. The structure achieves efficient discharge of water vapor to inhibit condensation of water vapor at a set of low temperatures, thus inhibiting occurrence of a flooding phenomenon, and hence providing high electric power generation performance at a set of low temperatures under a set of high humidification conditions. The structure holds water on a cathode catalyst layer side to retain a moisture level in the MEA so as to obtain high electric power generation performance at a set of high temperatures under a set of low-humidification conditions.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a diffusion layer structure of a solid polymer electrolyte fuel cell.    Solid polymer electrolyte fuel cell (1)    Diffusion layer structure (10)    Diffusion layer (11)    Microporous layer (12)    MEA (20)    Solid polymer electrolyte membrane (21)