An engine (8) is mounted to a vehicle body by means of vibration isolating mounts (8E), and a support member (15) is mounted to the engine (8). Vibration isolating members (20) are provided between this support member (15) and a mounting bracket (17) mounted to an exhaust gas treatment device (16). Accordingly, even in cases where the engine (8) has generated high-frequency vibrations, these vibrations can be damped by the vibration isolating mounts (8E) and the vibration isolating members (20). In consequence, treatment members constituting the exhaust gas treatment device (16), such as a catalyst, a filter, and a sensor, can be protected from the vibrations of the engine (8). In addition, as the exhaust gas treatment device (16) is provided with the mounting bracket (17), the vibration isolating members (20) can be reliably mounted to the exhaust gas treatment device (16) by means of the mounting bracket (17).