A downshift control apparatus for biasing a shift valve of a hydraulic control system of an automatic power transmission of an automotive vehicle toward a downshift position for raising the transmission gear shift points during kickdown or sudden deceleration condition of the vehicle, featuring a downshift valve which includes a valve spool movable between a first position passing a control fluid pressure to the shift valve and a second position discharging the fluid pressure from the shift valve, wherein the valve spool is urged toward the first position by the force of a spring and a fluid pressure developed in the valve in response to a kickdown condition or a sudden deceleration condition of the vehicle and toward the second position by a fluid pressure varying with the power output of the engine and a force resulting from a fluid pressure which acts on a differential pressure-acting area of the valve spool when the valve spool is held in or moving toward the second position thereof.