In an NC device having a function as a monitoring apparatus for a machine tool, a monitoring parameter and a retracting parameter which are set and inputted through an input unit by an operator, can be stored in a storage unit. When, for example, monitoring is performed by using a load on a main spindle as machine information, a machining monitoring unit displays a monitored state on a monitor, and compares a threshold value, of the load on the main spindle, according to which occurrence of abnormality is determined, and which is set in the monitoring parameter, and an instruction load generated by a machine operation instruction unit with each other, to determine whether or not abnormality has occurred. When abnormality is determined as having occurred, a retracting instruction is transmitted to a retracting instruction unit according to the retracting parameter, and display is performed on the monitor.