Two sets of assemblies (2a, 2b) are arranged so that the diesel particulate collection filter device (3) of the assembly (2a), the selective reduction catalyst device (4) of the assembly (2a), the selective reduction catalyst device (4) of the assembly (2b), and the diesel particulate collection filter device (3) of the assembly (2b) are arranged side by side in sequence. Exhaust tubes (6) are provided so as to extend upward from the exhaust openings (6a) of both the selective reduction catalyst device (4) of the assembly (2a) and the selective reduction catalyst device (4) of the assembly (2b). The two exhaust tubes (6) are located on an imaginary plane (E) perpendicular to the longitudinal directions (B1, B2) of the selective reduction catalyst devices (4) of the assemblies (2a, 2b). As a result of this configuration in which the two sets of assemblies (2a, 2b) are provided, the air intake position of an engine (10) can be easily set to a position at which the engine (10) is less likely to suck in exhaust gas discharged from the engine (10).