Abstract: A motor monitoring sensor is continuously operable at a lower cost. The motor monitoring sensor includes an acceleration sensor attachable to a motor to be monitored to detect vibration of the motor, a processor that generates state information indicating a state of the motor based on a detection value indicating the vibration of the motor detected by the acceleration sensor, a transmitter that transmits the generated state information to a host device, and a vibration-powered generator attachable to the motor to generate power with the vibration of the motor and supply the generated power to the acceleration sensor, the processor, and the transmitter.