A construction machine comprising: an engine; an air cleaner having an exhaust port and configured to filter air taken in by the engine; a pipe connected to the exhaust port of the air cleaner; a first structure; and a second structure other than the first structure; characterized by a seat plate on which the air cleaner and the pipe are mounted to form a subassembly; a device including an upper surface on which the subassembly is mounted, the device being configured to form, in cooperation with the installed subassembly, a device-assembly to be installed in a predetermined installation space; a fixing member for fixing the subassembly to the device, wherein: one of the seat plate and the surface of the device is provided with an aperture extending in a specific length direction and the other of the seat plate and the surface of the device is provided with a fit-in portion to be fitted into the aperture so as to be capable of relative displacement to the aperture in the length direction; the length direction is such a direction that the relative displacement of the fit-in portion to the aperture in the length direction allows the subassembly to be displaced between a first position and a second position, the first position being farther from the first structure, which is an obstacle to the installation of the subassembly into the installation space, and being closer to the second structure other than the first structure, than the second position; and the fixing member has both of a first fixing mode of fixing the subassembly to the device at the first position and a second fixing mode of fixing the subassembly to the device at the second position. an engine; an air cleaner having an exhaust port and configured to filter air taken in by the engine; a pipe connected to the exhaust port of the air cleaner; a first structure; and a second structure other than the first structure; a seat plate on which the air cleaner and the pipe are mounted to form a subassembly; a device including an upper surface on which the subassembly is mounted, the device being configured to form, in cooperation with the installed subassembly, a device-assembly to be installed in a predetermined installation space; a fixing member for fixing the subassembly to the device, wherein: one of the seat plate and the surface of the device is provided with an aperture extending in a specific length direction and the other of the seat plate and the surface of the device is provided with a fit-in portion to be fitted into the aperture so as to be capable of relative displacement to the aperture in the length direction; the length direction is such a direction that the relative displacement of the fit-in portion to the aperture in the length direction allows the subassembly to be displaced between a first position and a second position, the first position being farther from the first structure, which is an obstacle to the installation of the subassembly into the installation space, and being closer to the second structure other than the first structure, than the second position; and the fixing member has both of a first fixing mode of fixing the subassembly to the device at the first position and a second fixing mode of fixing the subassembly to the device at the second position. one of the seat plate and the surface of the device is provided with an aperture extending in a specific length direction and the other of the seat plate and the surface of the device is provided with a fit-in portion to be fitted into the aperture so as to be capable of relative displacement to the aperture in the length direction; the length direction is such a direction that the relative displacement of the fit-in portion to the aperture in the length direction allows the subassembly to be displaced between a first position and a second position, the first position being farther from the first structure, which is an obstacle to the installation of the subassembly into the installation space, and being closer to the second structure other than the first structure, than the second position; and the fixing member has both of a first fixing mode of fixing the subassembly to the device at the first position and a second fixing mode of fixing the subassembly to the device at the second position.