An object is to provide a voltage drop detection system which can accurately detect a drop in the voltage of a backup battery when a main power supply is off. A voltage drop detection system detects a drop in the voltage of a battery that supplies power to a first volatile memory when a main power supply is off, and the voltage drop detection system includes: a second volatile memory which is connected for the battery in parallel with the first volatile memory; a data writing unit which writes data in the second volatile memory when the main power supply is on; a data corruption detection unit which supplies, when the main power supply is off, power from the battery to the first volatile memory and the second volatile memory and which thereafter detects the corruption of the data written in the second volatile memory when the main power supply is on; and a voltage drop detection unit which detects the drop in the voltage of the battery based on the detection of the corruption of the data when the main power supply is on.