A turbo compressor, comprising: a casing (110, 210); a driving unit provided at an inner space of the casing (110, 210), and configured to generate a rotational force; a rotation shaft provided to penetrate the casing (110, 210), and configured to transfer the rotational force generated from the driving unit to outside; a compression unit (130, 140) provided outside the casing (110, 210), and configured to compress a fluid together with an impeller, a back pressure space (147, 247) provided between the compression unit (130, 140) and the casing (110, 210); a first back pressure passage configured to connect an outlet of the compression unit (130, 140) with the back pressure space (147, 247); and a back pressure control valve (173, 273) configured to selectively open and close a region between the first back pressure passage and the back pressure space (147, 247), characterized in that the turbo compressor further comprises a second back pressure passage configured to connect the outlet of the compression unit (130, 140) with the inner space of the casing (110, 210), wherein the second back pressure passage is diverged from a middle region of the first back pressure passage, and wherein the back pressure control valve (173, 273) is installed at a position where the second back pressure passage is diverged from the first back pressure passage, and is configured to selectively open and close the first back pressure passage or the second back pressure passage, according to a pressure of the fluid discharged from the compression unit (130, 140), and wherein the back pressure control valve (173, 273) has a first position where both of the first and second back pressure passages (171a, 171b) are closed, a second position where the first back pressure passage is open but the second back pressure passage is closed, and a third position where both of the first and second back pressure passages (171a, 171b) are open. a casing (110, 210); a driving unit provided at an inner space of the casing (110, 210), and configured to generate a rotational force; a rotation shaft provided to penetrate the casing (110, 210), and configured to transfer the rotational force generated from the driving unit to outside; a compression unit (130, 140) provided outside the casing (110, 210), and configured to compress a fluid together with an impeller, a back pressure space (147, 247) provided between the compression unit (130, 140) and the casing (110, 210); a first back pressure passage configured to connect an outlet of the compression unit (130, 140) with the back pressure space (147, 247); and a back pressure control valve (173, 273) configured to selectively open and close a region between the first back pressure passage and the back pressure space (147, 247), characterized in that the turbo compressor further comprises a second back pressure passage configured to connect the outlet of the compression unit (130, 140) with the inner space of the casing (110, 210), wherein the second back pressure passage is diverged from a middle region of the first back pressure passage, and wherein the back pressure control valve (173, 273) is installed at a position where the second back pressure passage is diverged from the first back pressure passage, and is configured to selectively open and close the first back pressure passage or the second back pressure passage, according to a pressure of the fluid discharged from the compression unit (130, 140), and wherein the back pressure control valve (173, 273) has a first position where both of the first and second back pressure passages (171a, 171b) are closed, a second position where the first back pressure passage is open but the second back pressure passage is closed, and a third position where both of the first and second back pressure passages (171a, 171b) are open.