To provide a method for improving a conventional device so that a generated signal is variable and reproducible, and an improved method for generating vibration particularly for the purpose of geophysical studies.

A vibration generator is a magnetostriction oscillator (12), which works axially, and in parallel to the longitudinal direction of a housing (11). A hard substance such as a rock lump to be examined abuts directly on devices (10 and 20). A compressive stress is applied to the magnetostriction oscillator (12), and the magnetostriction oscillator is operated so that excited vibration axially and in parallel to the longitudinal direction of the housing occurs inside the substance.