An apparatus for generating a depth image, the apparatus comprising: a light emitting unit for emitting light to an object; a light-receiving unit including a first gate and a second gate (G1,G2), the light receiving unit being configured to transform light emitted from the light emitting unit and reflected from the object into electric charge and to obtain light information based on the amount of the electric charge accumulated by the first and second gate; and a depth calculator to calculate a depth as the depth of the depth image based on first light information through fourth light information (nQ1-nQ4), wherein the first gate is configured to obtain first light information from the reflected light-based on a first pulse control signal applied to the first gate and the second gate is configured to obtain second light information from the reflected light based on a second pulse control signal applied to the second gate, and the first gate is configured to obtain third light information from the reflected light based on a third pulse control signal applied to the first gate and the second gate is configured to obtain fourth light information from a reflected light based on a fourth pulse control signal applied to the second gate wherein a phase difference between the first pulse control signal and the second pulse control signal is 180 degrees and a phase difference between the third pulse control signal and the fourth pulse control signal is 180 degrees; and wherein the depth calculator is configured to calculate the depth based on a first difference Y1 and a second difference Y2, the first difference Y1 being a difference between the first light information and the second light information and the second difference being a difference Y2 between the third light information and the fourth light information, characterized in that the depth calculator calculates, based on different schemes, the depth for each of a condition where both the first difference Y1 and the second difference Y2 are greater than or equal to zero, a condition where the first difference Y1 is less than zero and the second difference Y2 is greater than or equal to zero, a condition where both the first difference Y1 and the second difference Y2 are less than zero, and a condition where the first difference Y1 is greater than or equal to zero and the second difference Y2 is less than zero. a light emitting unit for emitting light to an object; a light-receiving unit including a first gate and a second gate (G1,G2), the light receiving unit being configured to transform light emitted from the light emitting unit and reflected from the object into electric charge and to obtain light information based on the amount of the electric charge accumulated by the first and second gate; and a depth calculator to calculate a depth as the depth of the depth image based on first light information through fourth light information (nQ1-nQ4), wherein the first gate is configured to obtain first light information from the reflected light-based on a first pulse control signal applied to the first gate and the second gate is configured to obtain second light information from the reflected light based on a second pulse control signal applied to the second gate, and the first gate is configured to obtain third light information from the reflected light based on a third pulse control signal applied to the first gate and the second gate is configured to obtain fourth light information from a reflected light based on a fourth pulse control signal applied to the second gate wherein a phase difference between the first pulse control signal and the second pulse control signal is 180 degrees and a phase difference between the third pulse control signal and the fourth pulse control signal is 180 degrees; and wherein the depth calculator is configured to calculate the depth based on a first difference Y1 and a second difference Y2, the first difference Y1 being a difference between the first light information and the second light information and the second difference being a difference Y2 between the third light information and the fourth light information, characterized in that the depth calculator calculates, based on different schemes, the depth for each of a condition where both the first difference Y1 and the second difference Y2 are greater than or equal to zero, a condition where the first difference Y1 is less than zero and the second difference Y2 is greater than or equal to zero, a condition where both the first difference Y1 and the second difference Y2 are less than zero, and a condition where the first difference Y1 is greater than or equal to zero and the second difference Y2 is less than zero.