By using a disc type resonator, a sensor detects a substance having a mass and the mass with high sensitivity. Moreover, it is preferable to detect a change in vibrations of a substance attached or adsorbed to an area having a vibration amplitude equal to or larger than a constant value. This disc type resonator can be fabricated by the MEMS technique by using single-crystal or polycrystalline Si as a structural material. To improve the attachment efficiency of molecules and the like to be detected, irregularity or a groove is preferably provided on the surface of the disc type resonator.