This paper proposes power-assist motion control of an electric wheelchair for a caregiver. Previous researches about power-assist motion of a wheelchair took operators as an object of study. But caregivers are aging as well as cared people due to growing proportion of elderly people. For detection of the caregiver's input, the reaction acceleration estimation observer is constructed. The motion of the wheelchair is identified to straight mode or cornering mode by rotational acceleration. The power-assist motion control is realized on each mode. Power-assist motion is performed on velocity. For calculation of the velocity, the acceleration generated by the caregiver's input is used. Numerical simulation is carried out to show the validity of the proposed method