An exhaust system for a steam turbine provided with an improved annular flow guide in a high or intermediate turbine. The improved flow guide reduces flow turbulence in an exhaust hood and reduces pressure loss to thereby improve turbine plant efficiency.The shape (vertically symmetric) of a flow guide 5A according to a conventional technology was modified into the shape (vertically asymmetric) of a flow guide 5 such that the length of a downstream flow guide portion 5d is greater than that of a upstream flow guide portion 5u. Numerical analyses were performed to find the optimum flow guide occupation ratio of the conventional technology and the corresponding total pressure loss coefficient. The obtained values were used as reference values. Further, the flow guide occupation ratio of the upstream flow guide portion 5u was set at 0.4 and the flow guide occupation ratio of the downstream flow guide portion 5d was set at 0.7; at values where the total pressure loss coefficient becomes lower than the reference value. The rectification effect of the flow guide can thus be enhanced.