A metal rod guide (30) supports a metal rod (1) that can be inclined at an
arbitrary angle, the support is instantaneously released to produce a
free fall state, and during the release period, a first end surface (2)
of the metal rod is impacted by a projectile (3) at the same angle as the
metal rod, generating an elastic wave pulse in the metal rod. A direct
current acceleration sensor (23) detects an acceleration arising when the
elastic wave pulse reflects at the other end surface (22) of the metal
rod. A strain gauge (25) provided on a side surface of the metal rod
and/or a laser interferometer (24) measure strain and end surface motion
and the measured values are processed to obtain a frequency response of
the direct current acceleration sensor and measure frequency
characteristics of the direct current acceleration sensor.