A drive force adjustment apparatus includes a differential gear, a motor, a first gear mechanism and a second gear mechanism. The input element, the first output element, the second output element, the motor input element, the fixed element, and the connecting element are expressed as points I, R, L, M, F and C on a graph, a ordinate of which shows the number of revolutions and a abscissa of which shows relative ratios of the number of revolutions of the elements. Length of L-I is equal to length of R-I, I is located between L and R on a straight line L-R, I is located between F and C on a straight line F-C, and R is located between C and M on a straight line C-M. Or, length of L-I is equal to length of R-I, I is located between L and R on a straight line L-R, L is located between M and C on a straight line M-C, and I is located between C and F on a straight line C-F.