To provide a vehicle decelerating power controller capable of smooth acceleration when deceleration is shifted to acceleration.

When changing to an accelerating condition by acceleration pedal operation during engine brake assist control, decelerating power (assist braking force) is reduced by applying decelerating power for prescribed relaxation time (t2-t0). A time variance in decelerating power at reduction is limited to a prescribed value or less. The prescribed value is larger, the larger a road surface gradient is in down-hill driving, and is set smaller, as the larger the gradient is in up-hill driving.