PURPOSE: To enable an alarm display to be carried out without delay, even if a periodical alarm signal is input, by constituting an alarm display device in such a way that when the time measured by an alarm signal off-time measuring part reaches a prescribed time, a mode changeover control part gives a command to a mode changeover part so as to change the mode into the standby mode.

CONSTITUTION: When a mode changeover control part 3 judges that all of the alarm signals being input are turned off, an off-time measuring part 2 measures the time elapsed after the signals have been turned off. The mode changeover control part 3 judges whether the alarm signal being input through an I/O 6 or 7 is turned on or not, and if the on-condition is continued, it judges whether or not the time being measured by the off-time measuring part 2 has reached a prescribed time. The mode changeover control part 3 gives a command to a display control part 5 to stop the alarm display being displayed by a display part 4 via an I/O 8. Then, the mode changeover control part 3 gives a command to a mode changeover part 1 to change over the mode from a normal mode to a standby mode.