To provide a method of estimating an oxygen concentration in a silicon single crystal, a method of manufacturing a silicon single crystal, and a silicon single crystal manufacturing apparatus capable of manufacturing silicon single crystals having constant quality by preventing polarization of the oxygen concentration in the silicon single crystal. A method of estimating an oxygen concentration in a silicon single crystal according to the present invention is provided with measuring a height (gap) of a melt surface of a silicon melt in a quartz crucible when pulling up a silicon single crystal while applying a lateral magnetic field to the silicon melt and estimating an oxygen concentration in the silicon single crystal from a minute variation in the height of the melt surface.