A standing-up assistance apparatus includes a first sensor that measures a muscle potential of a lower leg of a user, a second sensor that measures a knee angle of the user, a processor that determines whether starting to assist the user in a standing-up motion from a seated state is possible, based on, at least, the measured muscle potential and the measured knee angle, and outputs an instruction signal if the processor determines that starting to assist the user in the standing-up motion is possible, and an assistance mechanism. The assistance mechanism starts assisting the user in the standing-up motion when the assistance mechanism receives the instruction signal from the processor.