A double deck elevator comprising: a main traction unit for actuating a main frame to travel up and down in a hoistway of a building; an upper and a lower cage disposed inside the main frame; a cage-position adjusting drive unit provided to a top portion of the main frame and having a position adjusting drive sheave around which ropes suspending the respective upper and lower cage from the main frame are wound, for varying a distance between the cages (26, 28) by moving inside the main frame the cages (26, 28) vertically in mutually opposite directions by rotating the position adjusting drive sheave; characterized by a determination means for making determination by comparing whether at least one of cage-doorway floor-displacement levels detected by cages' detection sensors (37, 39) provided to the respective cages (26, 28) is equal to or larger than a floor-displacement-level threshold value that is stored beforehand in a storage means and is a reference for whether or not the floor displacement level to be corrected; a calculation means for performing calculations by substituting respective floor displacement levels of the upper and the lower cage successively into a plurality of conditions for correcting the floor displacement levels when the determination means determines that at least one of the cage-doorway floor-displacement levels is equal to or larger than the threshold value; and a selection means for selecting, when a relevant condition among the plurality of conditions holds true from a calculation result of the calculation means, either the main traction unit or the cage-position adjusting drive unit or both of the main traction unit and the cage-position adjusting drive unit to be actuated, according to the relevant condition, characterized in that when among the plurality of conditions, a condition of | (upper-cage floor displacement level) - (lower-cage floor displacement level) | / 2 ≤ (threshold value) holds true, the selection means selects the main traction unit to be actuated when among the plurality of conditions, a condition of | (upper-cage floor displacement level) + (lower-cage floor displacement level) | / 2 ≤ (threshold value) holds true, the selection means selects the cage-position adjusting drive unit to be actuated when among the plurality of conditions, conditions of |(upper-cage floor displacement level) + (lower-cage floor displacement level) / / 2 > (threshold value) and | (upper-cage floor displacement level) - (lower-cage floor displacement level) | 2 > (threshold value) hold true, the selection means selects the main traction unit and the cage-position adjusting drive unit to be actuated, and wherein the floor-displacement-level threshold value is non-zero. a main traction unit for actuating a main frame to travel up and down in a hoistway of a building; an upper and a lower cage disposed inside the main frame; a cage-position adjusting drive unit provided to a top portion of the main frame and having a position adjusting drive sheave around which ropes suspending the respective upper and lower cage from the main frame are wound, for varying a distance between the cages (26, 28) by moving inside the main frame the cages (26, 28) vertically in mutually opposite directions by rotating the position adjusting drive sheave; characterized by a determination means for making determination by comparing whether at least one of cage-doorway floor-displacement levels detected by cages' detection sensors (37, 39) provided to the respective cages (26, 28) is equal to or larger than a floor-displacement-level threshold value that is stored beforehand in a storage means and is a reference for whether or not the floor displacement level to be corrected; a calculation means for performing calculations by substituting respective floor displacement levels of the upper and the lower cage successively into a plurality of conditions for correcting the floor displacement levels when the determination means determines that at least one of the cage-doorway floor-displacement levels is equal to or larger than the threshold value; and a selection means for selecting, when a relevant condition among the plurality of conditions holds true from a calculation result of the calculation means, either the main traction unit or the cage-position adjusting drive unit or both of the main traction unit and the cage-position adjusting drive unit to be actuated, according to the relevant condition, characterized in that