Much interest has been focused on testing technology for structural architectures since the Hanshin-Awaji earthquake. The elastic wave method with hammering has been used for these tests so far. However, less stability of hammering and its response makes it difficult to detect deterioration and crack accurately. The other ultrasonic method with a piezoelectric device also has its limitations in the inhomogenous materials because the ultrasonic wave attenuates rapidly in them. A low frequency measurement in the frequency domain will be a solution to this, though it has been thought to be difficult because it requires large dimension of oscillator. A metal magnetostrictive material, whose magnetostrictive driving force is large, was employed and processed. The material has almost same the level of Young's modulus with steel. We applied additional compression stress on the device to enhance oscillating efficiency extraordinarily, by utilizing its strength which enabled the generation of a wide bandwidth of elastic wave even at low frequency in small size. Accordingly, it has become possible to measure the structures with a continuous elastic wave or pulse by controlling its frequency and power. To date tunnels, piles and roads have been measured and tested successfully by this new method, which is expected to be applied to various types of structures and materials.