A hydraulic pressure control system for an automatic transmission includes a multiple transmission gear mechanism having a plurality of gear stages and frictional elements for switching power transmitting paths in the transmission gear mechanism, a hydraulic control mechanism for controlling engagement and disengagement of the frictional elements to establish one of said gear stages, and a line pressure control device for controlling line pressure of the hydraulic control mechanism. A speed detecting device for detects a speed of an input element of the transmission gear mechanism during shift operation of the shift gear stage in the transmission gear mechanism, and a compensation device compensates the line pressure in accordance with signal from the speed detecting device. The line pressure is compensated by a learning control to reduce a torque shock due to the shift operation.