Disclosed is an exhaust gas purifier for an engine, comprising a bubble generator. The bubble generator mixes nano-to-micro size bubbles into a liquid reducing agent or a precursor thereof jetted and supplied through a jetting nozzle into a reducing agent supply system extended from a reducing agent tank to the jetting nozzle. When the liquid reducing agent or the precursor thereof is jetted and supplied through the jetting nozzle, the liquid reducing agent or the precursor thereof is disrupted by the bubbles, and, further, the bubbles are rapidly expanded and ruptured by a change in pressure and a change in temperature caused in the jetting and supply of the liquid reducing agent or the precursor thereof to accelerate the atomization of the liquid reducing agent or the precursor thereof.