To provide a turbo-molecular pump capable of reducing labor and cost required for axial deflection quantity measuring inspection, and a method for measuring axial deflection quantity in it.

Bolts 13a-13e include one reference bolt 13a provided with different magnetic characteristics from those of the other bolts 13b-13e. An eddy current displacement sensor is provided to measure magnetic characteristics of each of the bolts 13a-13e. The magnetic characteristics of the bolts 13a-13e when a rotor is rotated are measured as well as axial deflection quantity of the rotor by time series. Magnetic characteristic fluctuation and axial deflection quantity fluctuation by time series are thus compared.