A method of manufacturing a multistage exhaust turbocharger having a high-pressure stage turbocharger and a low-pressure stage turbocharger includes providing a high-pressure turbine housing of the high-pressure stage turbocharger, the high-pressure turbine housing being integrally formed with the exhaust manifold by casting or welding, assembling constituent parts of the high-pressure stage turbocharger using the high-pressure turbine housing as a reference, after the assembling constituent parts of the high-pressure stage turbocharger, attaching the low-pressure stage turbocharger to the high-pressure stage turbocharger by attaching a low-pressure turbine housing to a low-pressure turbine connection flange, and after the attaching the low-pressure stage turbocharger, attaching an air supply channel to connect between a supply air outlet of the low-pressure stage turbocharger and a supply air inlet of the high-pressure stage turbocharger, wherein the low-pressure turbocharger is disposed below the high-pressure turbocharger.