A muffler of a work machine in the form of an engine blower includes: a muffler body; and a diffuser that covers an exhaust outlet of exhaust gas provided on the muffler body. The diffuser has a diffusion space to diffuse the exhaust gas and an exhaust surface on which a plurality of exhaust circular holes are provided to exhaust the exhaust gas to an outside. An opening ratio provided by the exhaust holes of the exhaust surface is gradually increased from a portion corresponding to the exhaust opening toward an outer periphery of the exhaust surface.