A turbo compressor is provided that has first, second and third stage compressor blades rotated by a large gear shaft via an acceleration device, and includes a cast integral casing (1) which forms an acceleration unit cover housing the acceleration device, compression unit covers housing the compressor blades, and first, second and third stage cooler chambers (11a, 12a, 13a) which are arranged in parallel at a lower portion thereof, which communicate with the compressor unit covers by fluid passages, and into which first, second and third stage coolers are inserted from the side thereof. An oil tank (21) is integrally formed with the cast integral casing (1) so as to run along an insertion-directional innermost side of the coolers of the parallel-arranged first, second and third stage cooler chambers (11a, 12a, 13a).