To provide an automatic transmission controller capable of controlling a hydraulic pressure applied to a frictional element even when a modulate pressure is excessively raised due to a failure or the like.

In the automatic transmission controller, engagement and disengagement of a plurality of frictional elements 1-6 is controlled by a hydraulic pressure of a working fluid to change a speed stage. The controller is provided with a modulate pressure generating means 45 for reducing a line pressure being an initial pressure of the hydraulic pressure to be applied to the frictional elements 2-9, and generating the modulate pressure, solenoid valves 12, 18, 23, 28, 34 generating a command pressure using the modulate pressure as an initial pressure, pressure control valves 10, 16, 20, 26, 32 controlling the hydraulic pressure to be applied to the frictional elements 2-6 in accordance with the command pressure, and a pressure reducing means 46 for reducing the modulate pressure when the modulate pressure reaches an upper limit.