PURPOSE: To obtain a small level detector excellent in the stability by having a diaphragm vibrating in resonance with a piezo-electric element provided on the back thereof to detect changes in the vibration amplitude due to a powder, particulate, liquid or the like contacting the surface of the diaphragm through a vibro-voltage conversion element.

CONSTITUTION: A level detector is made up of a diaphragm 1, a vibrating piezo- electric element 3, a vibro-voltage conversion element 3', a weight 4 and electrodes 5aW5c all arranged on a circular frame 2. The surface of the diaphragm 1 is mounted facing the inside of a container 6 and an object 7 to be inspected such as a powder, particulate and liquid is fed to the container 6. An AC voltage is applied to the piezo-electric element 3 through the electrode 5b to vibrate in resonance the diaphragm 1 and changes in the vibration amplitude generated upon the contact of the object 7 being inspected with the diaphragm 1 are converted into an electrical signal through the electrodes 5a and 5c and the vibro- voltage conversion element 3' to detect level changes of the object 7 being inspected. Thus, a small level detector is obtained with an excellent stability.