PROBLEM TO BE SOLVED: To provide a main shaft bearing device effectively reducing supply frequency of lubricating water at low cost.SOLUTION: A main shaft bearing device 10 includes: a bearing tank 11 which is provided around a main shaft 6 and in which a lubricant is stored; and a bearing pad 20 provided in the bearing tank 11. The bearing pad 20 is at least partly immersed in the lubricant stored in the bearing tank 11 and receives a load in a radial direction of the main shaft 6. A gas phase space 31 above the lubricant stored in the bearing tank 11 is partitioned to an outside communication space 32 gas-communicating with the outside of the bearing tank 11, and a non-communicating space 33 not gas-communicating with the outside of the bearing tank 11 by a partitioning member 30.SELECTED DRAWING: Figure 2
