Provided is a method of producing a porous body of a water-insoluble polymer, the method being excellent in terms of simplicity and capable of suppressing formation of a skin layer. A method of producing a porous body of a water-insoluble polymer disclosed here includes the steps of: preparing a solution in which a water-insoluble polymer is dissolved in a mixed solvent containing a good solvent for the water-insoluble polymer and a poor solvent for the water-insoluble polymer; coating the solution on a substrate; coating a slurry containing insulating particles, a binder and a dispersion medium on the coated solution; and simultaneously drying the coated solution and the slurry to porosify the water-insoluble polymer. The poor solvent has a boiling point higher than a boiling point of the good solvent. The dispersion medium can dissolve the water-insoluble polymer.