A turbo compressor comprising: an open impeller (3,4) with a shroud (16,17) provided on a casing side; a rotary shaft which is supported by a radial magnetic bearing (7,8) and a thrust magnetic bearing (9,10); and a controller which includes load calculating means for calculating an axial direction thrust load (Ft) generated by a pressure distribution of the compressor in operation, and axial direction support position controlling means for controlling a gap between the impeller (3,4) and the shroud (16,17) by changing an axial direction support position of the rotary shaft determined by the thrust magnetic bearing (9,10) on the basis of the calculated axial direction thrust load (Ft); and means for detecting an axial direction position (26,27) of the rotary shaft installed at a position distant from a compression section, characterized in that the axial direction support position controlling means is configured to control the gap between the impeller (3,4) and the shroud (16,17) to at least two different target gaps including a minimum gap S1 and a gap S2 which is greater than the gap S1, and the controller includes first correcting means for detecting a temperature of a desired part, calculating a change amount of the gap between the impeller (3,4) and the shroud (16,17) from an axial length change amount of the rotary shaft due to thermal expansion and an axial direction change amount of the casing which sets a relative positional relationship between the shroud (16,17) and the impeller (3,4), and on the basis of this, correcting the axial direction support position. an open impeller (3,4) with a shroud (16,17) provided on a casing side; a rotary shaft which is supported by a radial magnetic bearing (7,8) and a thrust magnetic bearing (9,10); and a controller which includes load calculating means for calculating an axial direction thrust load (Ft) generated by a pressure distribution of the compressor in operation, and axial direction support position controlling means for controlling a gap between the impeller (3,4) and the shroud (16,17) by changing an axial direction support position of the rotary shaft determined by the thrust magnetic bearing (9,10) on the basis of the calculated axial direction thrust load (Ft); and means for detecting an axial direction position (26,27) of the rotary shaft installed at a position distant from a compression section, load calculating means for calculating an axial direction thrust load (Ft) generated by a pressure distribution of the compressor in operation, and axial direction support position controlling means for controlling a gap between the impeller (3,4) and the shroud (16,17) by changing an axial direction support position of the rotary shaft determined by the thrust magnetic bearing (9,10) on the basis of the calculated axial direction thrust load (Ft); and means for detecting an axial direction position (26,27) of the rotary shaft installed at a position distant from a compression section, characterized in that the axial direction support position controlling means is configured to control the gap between the impeller (3,4) and the shroud (16,17) to at least two different target gaps including a minimum gap S1 and a gap S2 which is greater than the gap S1, and the controller includes first correcting means for detecting a temperature of a desired part, calculating a change amount of the gap between the impeller (3,4) and the shroud (16,17) from an axial length change amount of the rotary shaft due to thermal expansion and an axial direction change amount of the casing which sets a relative positional relationship between the shroud (16,17) and the impeller (3,4), and on the basis of this, correcting the axial direction support position.