To provide a motor controller whose operation time is short due to its simple operation expression and which can detect collision with high sensitivity without erroneous detection even in case that an operation command changes suddenly, including harmonic components such as step waveform, or that there is vibration on load side or interference between shafts.

This motor controller, which drives a motor 13, based on the command of a motor control unit 11, and has a mechanism part 12 connected to the motor 13, is equipped with a simulation part 20 which has a motor model part 23 having simulated the motor 13, a mechanism part 22 having simulated the mechanism part, and a control part 21 having simulated the motor control unit, a quantity-of-state comparator 31 which compares the same quantities of the states of a real machine part 10 including the motor control unit 11, the motor 13, and the mechanism part 12, and the simulation part 20 with each other, and a contact detector 32 which detects the contact with outside by comparing the comparative value of the quantity of the state being the output of the-quantity-of-state comparator 31 with the preset detected threshold.