To provide an engine for a working machine using biomass ethanol also as fuel for a long period of time.

This engine for the working machine includes: a fuel tank 56 storing the fuel containing the biomass ethanol; a carburetor 100 generating an air-fuel mixture by mixing fuel introduced from the fuel tank into air; a combustion chamber 8 sucking and exploding the air-fuel mixture generated by the carburetor 100; a piston 4 reciprocated by explosion pressure generated in the combustion chamber 8; and a crankshaft 16 converting the reciprocation of the piston 4 into rotational movement and outputting the same. A primary filter 64 and a secondary filter 206 positioned downstream of the primary filter 64 which remove impurities in the fuel are provided in a fuel circulation process between the fuel tank 56 and the carburetor 100. The secondary filter 206 is configured to remove a remaining material without being decomposed in a biomass ethanol formation process.