A compression apparatus of the present disclosure includes an electrolyte membrane; an anode catalyst layer in contact with one of main surfaces of the electrolyte membrane; a cathode catalyst layer in contact with the other of the main surfaces of the electrolyte membrane; an anode gas diffusion layer in contact with the anode catalyst layer; a cathode gas diffusion layer in contact with the cathode catalyst layer; a cathode separator that is provided on the cathode gas diffusion layer; and a voltage applicator that applies voltage between the anode catalyst layer and the cathode catalyst layer. The compression apparatus generates compressed hydrogen by applying the voltage with the voltage applicator to move protons, taken out of an anode fluid supplied to the anode catalyst layer, to the cathode catalyst layer via the electrolyte membrane. The cathode gas diffusion layer includes a porous carbon sheet and is configured such that a porosity of a first surface layer in a side of the cathode separator is lower than a porosity of a layer inward from the first surface layer.