A turbo compressor, comprising: a casing ; a driving unit provided at an inner space of the casing , and configured to generate a rotational force; a rotation shaft provided to penetrate the casing , and configured to transfer the rotational force generated from the driving unit to outside; a compression unit provided outside the casing , and configured to compress a fluid together with an impeller, a back pressure space provided between the compression unit and the casing ; a first back pressure passage configured to connect an outlet of the compression unit with the back pressure space ; and a back pressure control valve configured to selectively open and close a region between the first back pressure passage and the back pressure space , characterized in that the turbo compressor further comprises a second back pressure passage configured to connect the outlet of the compression unit with the inner space of the casing , 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 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 , and wherein the back pressure control valve has a first position (P1) where both of the first and second back pressure passages are closed, a second position (P2) where the first back pressure passage is open but the second back pressure passage is closed, and a third position (P3) where both of the first and second back pressure passages are open. a casing ; a driving unit provided at an inner space of the casing , and configured to generate a rotational force; a rotation shaft provided to penetrate the casing , and configured to transfer the rotational force generated from the driving unit to outside; a compression unit provided outside the casing , and configured to compress a fluid together with an impeller, a back pressure space provided between the compression unit and the casing ; a first back pressure passage configured to connect an outlet of the compression unit with the back pressure space ; and a back pressure control valve configured to selectively open and close a region between the first back pressure passage and the back pressure space , characterized in that the turbo compressor further comprises a second back pressure passage configured to connect the outlet of the compression unit with the inner space of the casing , 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 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 , and wherein the back pressure control valve has a first position (P1) where both of the first and second back pressure passages are closed, a second position (P2) where the first back pressure passage is open but the second back pressure passage is closed, and a third position (P3) where both of the first and second back pressure passages are open. <EOS>