A cordless surgical device includes a battery and a memory that stores data in which, with each of a plurality of energy output modes in which living tissue is treated by applying energy to the living tissue, a minimum power necessary to execute the energy output mode is associated, and a processor. The processor monitors a remaining power in the battery, selects an energy output mode in which the minimum power is less than the remaining power in the battery from among the energy output modes, and executes the selected energy output mode. The energy output modes include a normal output mode and an urgent output mode between which types of energy applied to the living tissue are the same. The minimum power corresponding to the normal output mode is higher than the minimum power corresponding to the urgent output mode.