The present invention provides a method and device for cooling steam turbine generating equipment. The disclosed method and device efficiently cool the area near the part where working steam, that is the high temperature atmosphere of a countercurrent single casing steam turbine wherein multiple steam turbines are housed in a single casing, is introduced. In the countercurrent single casing steam turbine (40) wherein a high-pressure turbine part (31a) and a medium-pressure turbine part (32a) are housed in a single casing, the high-pressure turbine part (31a) and the medium-pressure turbine part (32a) are partitioned with a dummy ring (10), and a cooling steam supply path (101) and a cooling steam exhaust path (103) are provided in the dummy ring (10) in the radial direction. Bleed steam or exhaust steam (s1) from the high-pressure turbine part (31a) that is cooler than steam that has passed through the pre-side stator blade (8a1) and has a higher pressure than said steam is supplied to the cooling steam supply path (101). By allowing the steam s1 to spread into gaps (721) and (723), the cooling effects on the dummy ring (10) and turbine rotor (7) are improved. Cooling steam (s1) after being provided for cooling is exhausted from the cooling steam exhaust path (103) into an exhaust steam pipe (44) that supplies steam to a later-stage steam turbine.