An apparatus (100, 200) for obtaining a three-dimensional, 3D, image by using infrared rays, IRs, together with visible light, the apparatus (100, 200) comprising: a light transmitting unit for emitting IR structured light to an object to be recognized; a light receiving unit comprising an RGB-IR sensor for receiving IRs and visible light reflected from the recognized object; a processor for obtaining 3D image information including depth information and a visible light image of the recognized object by using each of the infrared rays and the visible light, which are received by the light receiving unit; and a lighting unit for controlling a lighting cycle of the IR structured light, wherein the lighting unit is configured to: control the lighting cycle of the IR structured light to remove interference between a visible light measurement time period T1 and an infrared measurement time period T2 by separating the visible light measurement time period T1 and the infrared measurement time period T2 from each other, and repeat the visible light measurement time period T1 and the infrared measurement time period T2 wherein the time periods, T1 and T2, have the same length by considering brightness of ambient light when the brightness of the ambient light is greater than a predetermined conventional reference value Th2, wherein the visible light measurement time period T1 indicates the visible light exposure period, and wherein the infrared measurement time period T2 indicates the infrared exposure period, characterized in that the lighting unit is further configured to control the lighting cycle of the IR structured light to allow the visible light measurement time period T1 to be longer than the infrared measurement time period T2 when the brightness of the ambient light is greater than a predetermined minimum reference value Th1 and less than the predetermined conventional reference value Th2, wherein the processor is configured to obtain infrared differential images (e0 to e4) by subtracting infrared images obtained for the visible light measurement time period T1 (d0 to d4) from infrared images obtained for the infrared measurement time period T2 (i0 to i4) when the brightness of the ambient light is greater than the predetermined minimum reference value Th1. a light transmitting unit for emitting IR structured light to an object to be recognized; a light receiving unit comprising an RGB-IR sensor for receiving IRs and visible light reflected from the recognized object; a processor for obtaining 3D image information including depth information and a visible light image of the recognized object by using each of the infrared rays and the visible light, which are received by the light receiving unit; and a lighting unit for controlling a lighting cycle of the IR structured light, wherein the lighting unit is configured to: control the lighting cycle of the IR structured light to remove interference between a visible light measurement time period T1 and an infrared measurement time period T2 by separating the visible light measurement time period T1 and the infrared measurement time period T2 from each other, and repeat the visible light measurement time period T1 and the infrared measurement time period T2 wherein the time periods, T1 and T2, have the same length by considering brightness of ambient light when the brightness of the ambient light is greater than a predetermined conventional reference value Th2, control the lighting cycle of the IR structured light to remove interference between a visible light measurement time period T1 and an infrared measurement time period T2 by separating the visible light measurement time period T1 and the infrared measurement time period T2 from each other, and repeat the visible light measurement time period T1 and the infrared measurement time period T2 wherein the time periods, T1 and T2, have the same length by considering brightness of ambient light when the brightness of the ambient light is greater than a predetermined conventional reference value Th2, wherein the visible light measurement time period T1 indicates the visible light exposure period, and wherein the infrared measurement time period T2 indicates the infrared exposure period, characterized in that the lighting unit is further configured to control the lighting cycle of the IR structured light to allow the visible light measurement time period T1 to be longer than the infrared measurement time period T2 when the brightness of the ambient light is greater than a predetermined minimum reference value Th1 and less than the predetermined conventional reference value Th2, wherein the processor is configured to obtain infrared differential images (e0 to e4) by subtracting infrared images obtained for the visible light measurement time period T1 (d0 to d4) from infrared images obtained for the infrared measurement time period T2 (i0 to i4) when the brightness of the ambient light is greater than the predetermined minimum reference value Th1.