To provide a control device for machine tool easy to control the number of revolution.

A hydraulic motor 16 has a variable displacement volume corresponding to the pilot pressure P2 to be led in. A pilot pressure sensor 40 for detecting the pilot pressure P2 to the hydraulic motor 16 is provided. An electromagnetic control valve 38 for controlling the pilot pressure in response to the command signal is provided. A set number of revolution of the hydraulic motor 16 is computed for display on the basis of the pilot pressure P2 detected by the pilot pressure sensor 40 and the engine speed of an internal combustion engine 44. A supply pressure sensor 42 for detecting the supply pressure P3 to the hydraulic motor 16 is provided, and the electromagnetic control valve 38 is controlled so as to control the supply pressure P3 at the preset boundary pressure P4.