The purpose of the present invention is to provide a manufacturing method for an exhaust gas purification device that can uniformly coat a honeycomb substrate with slurry even when using a low viscosity slurry. The present invention pertains to a manufacturing method for an exhaust gas purification device that includes providing a slurry for catalyst layer formation from a shower nozzle onto a honeycomb substrate, coating the honeycomb substrate with the slurry, and firing the honeycomb substrate coated with the slurry, wherein the viscosity of the slurry at a shear rate of 4 s−1 is 800 mPA·s or less, the shower nozzle has a plurality of discharge openings for discharging the slurry, the relationship of the spacing a) of the discharge openings and the diameter b) of the liquid drops formed when starting supply of the slurry is 0.85