Parking lock device and method for automatic transmission

A parking lock device comprises a parking lock mechanism (12) which locks an output shaft (1A) of a vehicle automatic transmission (1) when a shift lever (18) is changed over to a parking range, and an automatic brake device (14) which brakes the vehicle. When the shift lever (18) is changed over to the parking range at a vehicle speed is not less than a predetermined vehicle speed VSP1, a control unit (15) first operates the automatic brake device (14) to decelerate the vehicle and then operates the parking lock mechanism (12) after the vehicle speed has dropped to less than the predetermined vehicle speed VSP1. By this deceleration, the shock given to the vehicle by locking the output shaft (1A) while the vehicle is running is suppressed. The load of the parking lock mechanism due to the locking of the output shaft (1A) is also alleviated.