A mobile object control device controls an electric motor assisting traveling of a mobile object. The mobile object control device includes a rolling resistance calculation section, a power loss calculation section, and an assist force calculation section. The rolling resistance calculation section calculates a rolling resistance based on a set weight set by a user. The power loss calculation section calculates a power loss caused until a power outputted from the electric motor is transmitted to a drive wheel. The assist force calculation section calculates an assist force of the electric motor based on an acceleration of the mobile object, the set weight, the rolling resistance calculated by the rolling resistance calculation section, the power loss calculated by the power loss calculation section, and an assist ratio.