An automatic transmission line pressure control system controls line pressure in an automatic transmission equipped with a torque convertor for hydraulically coupling and uncoupling friction coupling elements of the automatic transmission. The automatic transmission line pressure control system regulates line pressure for selectively coupling and uncoupling the friction coupling elements so as to shift the automatic transmission into desired speed gears. The line pressure is forcibly dropped to a level lower than a level present before an occurrence of a manual shift-down operation when a shift-down sensor detects the occurrence of a manual shift-down. The line pressure is then raised as a speed sensor detects an increase in rotational speed transmitted the automatic transmission, thereby shifting the automatic transmission into desired speed gears.