A turbo compressor having first, second, and third stage compressor blades (8, 9, 10) rotated by a shaft via an acceleration device, the shaft being connected to a large gear of the acceleration device, the turbo compressor comprising: a cast integral casing comprising: an acceleration unit cover housing the acceleration device; compression unit covers (8a, 9a, 10a) housing the respective compressor blades (8, 9, 10); and first, second, and third stage cooler chambers (11a, 12a, 13a), which are arranged in parallel at a lower portion of the cast integral casing, into which first, second, and third stage coolers (11, 12, 13) are respectively inserted from a side of the cast integral casing, and which are spatially connected to the compression unit covers (8a, 9a, 10a) via fluid passages (14, 15, 16, 17, 18), the turbo compressor being characterised in that an oil tank is integrally formed with the cast integral casing so as to run along an insertion-directional innermost side of the coolers (11, 12, 13) of the first, second, and third stage cooler chambers (11a, 12a, 13a) arranged in parallel, wherein, among the first, second, and third stage cooler chambers (11a, 12a, 13a) arranged in parallel, the cooler chamber located at a parallel-arrangement-directional end of the cooler chambers (11a, 12a, 13a) extends while avoiding the oil tank, and an extension part thereof has a fluid outlet and a drain outlet. a cast integral casing comprising: an acceleration unit cover housing the acceleration device; compression unit covers (8a, 9a, 10a) housing the respective compressor blades (8, 9, 10); and first, second, and third stage cooler chambers (11a, 12a, 13a), which are arranged in parallel at a lower portion of the cast integral casing, into which first, second, and third stage coolers (11, 12, 13) are respectively inserted from a side of the cast integral casing, and which are spatially connected to the compression unit covers (8a, 9a, 10a) via fluid passages (14, 15, 16, 17, 18), the turbo compressor being characterised in that an oil tank is integrally formed with the cast integral casing so as to run along an insertion-directional innermost side of the coolers (11, 12, 13) of the first, second, and third stage cooler chambers (11a, 12a, 13a) arranged in parallel, an acceleration unit cover housing the acceleration device; compression unit covers (8a, 9a, 10a) housing the respective compressor blades (8, 9, 10); and first, second, and third stage cooler chambers (11a, 12a, 13a), which are arranged in parallel at a lower portion of the cast integral casing, into which first, second, and third stage coolers (11, 12, 13) are respectively inserted from a side of the cast integral casing, and which are spatially connected to the compression unit covers (8a, 9a, 10a) via fluid passages (14, 15, 16, 17, 18), the turbo compressor being characterised in that an oil tank is integrally formed with the cast integral casing so as to run along an insertion-directional innermost side of the coolers (11, 12, 13) of the first, second, and third stage cooler chambers (11a, 12a, 13a) arranged in parallel, wherein, among the first, second, and third stage cooler chambers (11a, 12a, 13a) arranged in parallel, the cooler chamber located at a parallel-arrangement-directional end of the cooler chambers (11a, 12a, 13a) extends while avoiding the oil tank, and an extension part thereof has a fluid outlet and a drain outlet.