Abstract: A rotation measuring device 10 including a proximity switch 14 detecting rotational speed of an object to be measured, a controller 11 receiving pulse signals from the switch 14, and a display 34 connected to the controller 11, the controller 11 including a rotational speed calculation means, the device 10 calculating the rotational speed based on the pulse signals by the rotational speed calculation means and indicating the rotational speed on the display 34, the controller 11 including: a standard rotational speed setting means for setting a measured rotational speed as a standard rotational speed by button operation; an upper and lower limits setting means for setting maximum and minimum rotational speeds based on the standard rotational speed; and a warning signal generating means generating warning signal outputs when the rotational speed is over the maximum rotational speed or below the minimum rotational speed.