To clarify the mechanism of increase in the power loss for gas-liquid two-phase flow driven by a rotating disk in the cylindrical container, we investigated the influence of kinematic viscosity on torque acting on the surface of the rotating disk. For high viscous liquids, the torque on the disk in the two-phase flow is smaller than that in the single phase which is full of liquid, while for low viscous liquids, the torque in the two-phase flow is larger. We measured the spatial distribution of turbulent intensity via 2D-PIV, and visualized the vortical structure appearing near the free surface and the static casing in the two-phase flow condition via stereo-PTV. We discusse the effect of modifications in flow field on the torque changes in the two-phase flow condition.