The micromechanical device comprises a mobile beam attached via the two ends thereof to a rigid frame comprising two arms each having two ends. The ends of an arm are respectively secured to the two ends of the mobile beam. Each arm has a middle part arranged between the two ends of the corresponding arm. A rear face of the middle part of each arm is attached to a base support. The frame comprises at least one stressed element enabling the state of stress of the beam to be adjusted. The stressed element can be centered between the front face and the rear face of the corresponding arm. The frame can comprise pairs of front and rear stressed elements arranged facing one another respectively on the front face and on the rear face of the arms.