A ratio of cross sectional area A of a scroll passage to a scroll radius R (A/R) can be increased without increasing the size of a turbine casing and with very simple construction. An exhaust turbine capacity can thus be increased, so that a variable-throat exhaust turbocharger in which the engine output can be increased results. The turbocharger has a nozzle throat area varying mechanism of which a nozzle assembly unit is composed. A plurality of nozzle vanes are supported rotatably by an annular nozzle mount and an annular nozzle plate is connected to the nozzle mount by a plurality of nozzle supports to sandwich the nozzle vanes. The nozzle plate is located in the scroll chamber by attaching the nozzle assembly unit to the turbine casing to allow the nozzle plate to form part of the inside sidewall face of the scroll chamber and a wall face of the annular flow passage.