An information record and playback apparatus configured to perform record and playback operations of an optical disk which is provided with data recording tracks having a surface wobbled at a predetermined frequency and a plurality of prepits formed with a predetermined phase relation to the position for data recording. The alarming unit includes a resonator housing defining a cavity in which is placed at least one resonator and a bias piece covered by a housing cover affixed to the resonator housing. A pressure sensor measures atmospheric pressure and inner pressure of the ink chamber.