A transmission control device, for a road vehicle with an engine and a transmission which has a gearbox which includes several fluid pressure activated friction engaging mechanisms and which can provide at least three forward speed stages according to selective supplying of actuating pressures to the friction engaging mechanisms, practices a transmission control method. An electrically actuated hydraulic pressure control device selectively supplies actuating pressures to the friction engaging mechanisms so as to engage any one of the forward speed stages i.e. gear ratios. An electronic control system repeatedly at short time intervals receives from a road speed sensor and an engine load sensor signals representative of road speed and of engine load, then determines a target speed stage, then determines a decided speed stage, and then energizes the hydraulic pressure control device to engage the decided speed stage. The decided speed stage is determined so as to cause, when the actual speed stage and the target speed stage differ by less than two speed stages, immediate shifting of the gearbox to the target speed stage; and is also determined so as to cause, when the actual speed stage and the target speed stage differ by two or more speed stages, at least sometimes shifting of the gearbox by steps of one speed stage at a time to the target speed stage, the shifts by steps being separated in time by at least a predetermined first time interval.