A steering assist apparatus for a vehicle, which is to be applied to the vehicle comprising a steering device, the steering device comprising: a steering wheel to be operated by a driver; steered wheels (20L, 20R); and a transmission device configured to transmit a force and a displacement relating to steering between the steering wheel and the steered wheels (20L, 20R), the steering assist apparatus comprising: an adjustment force (Ta) applying device configured to apply an adjustment force for adjusting a force relating to the steering to the transmission device; a control device configured to control the adjustment force (Ta) to be applied by the adjustment force applying device to the transmission device; a steering angle detection device configured to detect a steering angle (θ); and a steering torque detection device configured to detect a steering torque, characterized in that the control device is configured to acquire a steering angular velocity (dθ), a derivative (ddθ) of the steering angular velocity, and a derivative (dT) of the steering torque, calculate, assuming the steering wheel, the transmission device, the adjustment force applying device, and the steered wheel (20L, 20R) as a steering system, a change rate (dDE) of an energy of the steering system based on a product of the steering angular velocity (dθ) and the derivative (ddθ) of the steering angular velocity, a product of the steering angular velocity (dθ) and the steering torque, and a product of the steering angle y (θ) and the derivative (dT) of the steering torque, and control the adjustment force (Ta) based on the change rate (dDE) of the energy of the steering system. the steering device comprising: a steering wheel to be operated by a driver; steered wheels (20L, 20R); and a transmission device configured to transmit a force and a displacement relating to steering between the steering wheel and the steered wheels (20L, 20R), a steering wheel to be operated by a driver; steered wheels (20L, 20R); and a transmission device configured to transmit a force and a displacement relating to steering between the steering wheel and the steered wheels (20L, 20R), the steering assist apparatus comprising: an adjustment force (Ta) applying device configured to apply an adjustment force for adjusting a force relating to the steering to the transmission device; a control device configured to control the adjustment force (Ta) to be applied by the adjustment force applying device to the transmission device; a steering angle detection device configured to detect a steering angle (θ); and a steering torque detection device configured to detect a steering torque, characterized in that an adjustment force (Ta) applying device configured to apply an adjustment force for adjusting a force relating to the steering to the transmission device; a control device configured to control the adjustment force (Ta) to be applied by the adjustment force applying device to the transmission device; a steering angle detection device configured to detect a steering angle (θ); and a steering torque detection device configured to detect a steering torque, characterized in that the control device is configured to acquire a steering angular velocity (dθ), a derivative (ddθ) of the steering angular velocity, and a derivative (dT) of the steering torque, calculate, assuming the steering wheel, the transmission device, the adjustment force applying device, and the steered wheel (20L, 20R) as a steering system, a change rate (dDE) of an energy of the steering system based on a product of the steering angular velocity (dθ) and the derivative (ddθ) of the steering angular velocity, a product of the steering angular velocity (dθ) and the steering torque, and a product of the steering angle y (θ) and the derivative (dT) of the steering torque, and control the adjustment force (Ta) based on the change rate (dDE) of the energy of the steering system.