A servo signal inspection device and a method for detecting servo signal are provided which can measure and evaluate quality of the servo signal on a magnetic tape with a sufficient resolution. The device includes a servo signal inspecting head, a peak detecting means, a time interval measuring means and an inspection means, wherein a period T [s] of a standard clock signal used in the time interval measuring means and a running speed v [m/s] of the magnetic tape at the servo signal inspecting head satisfy the following relationship: T.times.v<80 nm.