In a sensor device which detects pressure variations owing to displacements of a body surface of a subject by respiration through variations of the output impedance of a piezoelectric vibrator, the pressure variations can be more efficiently transmitted to the piezoelectric vibrator. The sensor device, attached to a subjects body surface, comprises a contact piece contacting the body surface a displacement-signal convertor which converts the displacements of the body surface into electrical signals and an outputting device which outputs the electrical signals to an external unit the sensor device is clamped between the body surface of the subject and an upper edge portion of a subjects bottom garment, and the contact piece is arranged in one side surface of a housing, and a stopping member which can be attached with the upper edge portion of the bottom garment in the other side surface of the housing.
