A travelling speed control apparatus of construction machinery, comprising: first and second hydraulic pumps (110, 120) configured to supply hydraulic oil to first and second travel motors (10, 20) respectively; first and second pressure sensors (610, 620) installed in hydraulic lines (210, 220) of the first and second hydraulic pumps (110, 120) configured to detect first and second pump pressures acting on the first and second travel motors (10, 20) respectively; a selection portion through which an operator selects a travelling speed auto control mode, at least one travelling speed control valve switchable by an inputted travelling speed control signal configured to adjust a swash plate angle of each of the first and second travel motors (10, 20); a travelling speed controller configured to compare a difference value between the first and second pump pressures with a predetermined value, output the travelling speed control signal to the travelling speed control valve configured to shift rotational speed steps of the first and second travel motors (10, 20) from second step to first step when the travelling speed controller receives a selection signal of the travelling speed auto control mode from the selection portion, one of the first and second pump pressures is 0 bar, and the difference value is greater than the predetermined value, and, when it is determined that the first and second pump pressures are less than a predetermined value, output the travelling speed control signal to the travelling speed control valve configured to shift the rotational speed steps of the first and second travel motors (10, 20) from the first speed to the second speed to the travelling speed control valve. first and second hydraulic pumps (110, 120) configured to supply hydraulic oil to first and second travel motors (10, 20) respectively; first and second pressure sensors (610, 620) installed in hydraulic lines (210, 220) of the first and second hydraulic pumps (110, 120) configured to detect first and second pump pressures acting on the first and second travel motors (10, 20) respectively; a selection portion through which an operator selects a travelling speed auto control mode, at least one travelling speed control valve switchable by an inputted travelling speed control signal configured to adjust a swash plate angle of each of the first and second travel motors (10, 20); a travelling speed controller configured to compare a difference value between the first and second pump pressures with a predetermined value, output the travelling speed control signal to the travelling speed control valve configured to shift rotational speed steps of the first and second travel motors (10, 20) from second step to first step when the travelling speed controller receives a selection signal of the travelling speed auto control mode from the selection portion, one of the first and second pump pressures is 0 bar, and the difference value is greater than the predetermined value, and, when it is determined that the first and second pump pressures are less than a predetermined value, output the travelling speed control signal to the travelling speed control valve configured to shift the rotational speed steps of the first and second travel motors (10, 20) from the first speed to the second speed to the travelling speed control valve.