A method of manufacturing a steam turbine rotor which includes an ultra-high temperature side portion in which ultra-high temperature steam flows and a high temperature side portion in which high temperature steam flows, the manufacturing method including the steps of: preparing a first electrode having a chemical composition corresponding to a chemical composition of a heat resistant alloy making up the ultra-high temperature side portion and a second electrode having a chemical composition corresponding to a chemical composition of the high temperature side portion; tentatively joining together joints of the electrodes, with the joints of the electrodes made smaller in cross sectional area than other electrode portions; subjecting the tentatively joined first and second electrodes to an ESR process to obtain an ESR ingot and forging the ingot into a shape of a rotor to obtain a rotor forging; and heat-treating the rotor forging to obtain a rotor blank and manufacturing the steam turbine rotor from the rotor blank.