PURPOSE: To permit an extensible mast structure for a lift truck to continue its transitional movement to upward or downward movement on a load carrying structure.

CONSTITUTION: This mast structure is provided with a fixed mast, a movable mast, a load carrying structure 20 which can be moved vertically by the movable mast, and a lift means which comprises a first jack 25 and a second jack 33. The two jacks have selectively operated continuous cross-sectional areas disposed to sequence movement of the primary jack to move the load carrying carriage before the secondary jack operates the mast structure 10, and the first jack assists the secondary jack and extends the mast structure during the remainder of its stroke while continuing to lift the load carrying structure relative to the mast structure. Then the secondary jack further continuously extends the mast structure.