a motor having an output rotating shaft and a motor winding for exerting a rotation drive force to the output rotating shaft;

a rotor connected to the output rotating shaft for holding a sample to be separated;

a rotor chamber containing the rotor and having an opening portion at an upper face thereof;

a door openably and closably provided to the opening portion for opening or closing the opening portion of the rotor chamber;

a door lock mechanism for restricting opening/closing of the door;

a motor drive circuit having a power converting circuit for supplying a drive power source to the motor winding;

a control circuit apparatus for controlling the door lock mechanism and the motor drive circuit;

a housing containing the rotor chamber, the door lock mechanism, the motor drive circuit, and the control circuit apparatus and mounted with the door in correspondence with the opening portion of the rotor chamber; and

an opening/closing apparatus electrically connected to a power supply line to the power converting circuit of the motor drive circuit and made to be electrically conductive or nonconductive,

wherein the control circuit apparatus makes the opening/closing apparatus nonconductive when the door lock mechanism does not lock the door,

wherein the motor drive circuit includes a converter electrically connected to a power supply line to the power converting circuit for converting an alternating current power supply line into a direct current power supply line, said converter including a rectifying circuit and a smoothing circuit,

wherein the direct current power supply line includes a supply line for electrically connecting a rectified output of the rectifying circuit to the smoothing circuit, and

wherein the opening/closing apparatus is electrically connected to the supply line between the rectifying circuit and the smoothing circuit.