A controller switches a measurement unit from a non-measurement state to a measurement state to start measurement processing of the measurement target physical amount when a trigger condition having a lowest variation level for a steady state is satisfied in plural trigger conditions set according to a trigger physical amount detected by a trigger detector, and the controller interrupts currently-performed measurement processing to start measurement processing corresponding to a trigger condition having a higher variation level when the trigger condition having the variation level for the steady state higher than that of the trigger condition corresponding to the currently-performed measurement processing is satisfied during performance of the measurement processing.