A road slope estimating device which is mounted on a vehicle and estimates a slope of a road on which the vehicle is traveling, the vehicle including a motor and a transmission capable of changing a shift speed by an engagement switching operation of disengaging one of a plurality of engagement elements and engaging another one of the plurality of engagement elements, and outputting power from the motor via the transmission to travel. An estimating section carries out first road slope estimation from the computed output torque and acceleration of the vehicle until transfer of torque is handed over from the engagement element to be disengaged of the plurality of engagement elements to the engagement element to be engaged. Second road slope estimation is estimated from the computed output torque and the acceleration of the vehicle when the handover of the transfer of torque is carried out.