To provide an automatic analyzer capable of performing self-diagnosis when abnormalities occur in a device to reduce a device maintenance time.

A reference voltage source 18 generates a reference voltage. A relay 17 can select the reference voltage generated by the reference voltage source and the output signal voltage of a pressure sensor 14. The drive control part of a microcomputer 20 outputs a relay switching signal for switching two inputs by the relay 17. A determination part determines that a pressure sensor signal input substrate 15 is abnormal when the drive control part selects the reference voltage and an input signal voltage is beyond a regulated range.