A machine tool controller includes: a voltage detection unit which detects a voltage value of an input power supply; a time measurement unit which measures an occurrence time and a duration time when a voltage drop state occurs with respect to the voltage value; an abnormality determination unit which determines whether a low voltage abnormality or a power failure occurs with respect to the input power supply based on the voltage value and the duration time of the voltage drop state; a machining management unit which acquires a machining condition command and machining information of the machine tool; and a storage unit which stores the voltage value detected by the voltage detection unit, the occurrence time of the voltage drop state measured by the time measurement unit, and the machining information when the abnormality determination unit determines that the low voltage abnormality occurs with respect to the input power supply.