A vertical machining center, in which a table and a tool spindle are movable relative to each other in an X axis direction, a Y axis direction, and a Z axis direction, comprising: an angle tool holder (200, 200a, 200b) attachable and detachable with respect to the tool spindle, a tool unclamping operation device (370, 380), a tool changer, the angle tool holder (200, 200a, 200b) comprising: a shank to be inserted into the tool spindle; a spindle comprising an axis perpendicular to an axis of the shank; a housing rotatably supporting the shank and the spindle, the housing comprising an internal transmission mechanism configured to transmit drive force of the shank to the spindle; a collet disposed on the spindle and configured to clamp a tool; a draw bar disposed in the spindle to move forward and backward to clamp and unclamp the collet; and a spring mechanism configured to bias the draw bar in a direction in which the collet clamps the tool; the tool unclamping operation device (370, 380) comprising: restriction means (380, 510, 610) for restricting a portion of the angle tool holder (200, 200a, 200b) and for receiving force in an axial direction of the spindle; and a hydraulic piston configured to press the draw bar of the angle tool holder (200, 200a, 200b), wherein the tool attached to the angle tool holder (200, 200a, 200b) is changed by the tool changer and the tool unclamping operation device, characterized in that the tool unclamping operation device (370, 380) further comprises an angle tool holder rest (360, 500, 600), the restriction means (380, 510, 610) is disposed on the angle tool holder rest (360, 500, 600), and that a point of application of force that the restriction means (380, 510, 610) receives when the hydraulic piston presses the draw bar is one point on a vertical plane within which the axis of the spindle is contained. an angle tool holder (200, 200a, 200b) attachable and detachable with respect to the tool spindle, a tool unclamping operation device (370, 380), a tool changer, the angle tool holder (200, 200a, 200b) comprising: a shank to be inserted into the tool spindle; a spindle comprising an axis perpendicular to an axis of the shank; a housing rotatably supporting the shank and the spindle, the housing comprising an internal transmission mechanism configured to transmit drive force of the shank to the spindle; a collet disposed on the spindle and configured to clamp a tool; a draw bar disposed in the spindle to move forward and backward to clamp and unclamp the collet; and a spring mechanism configured to bias the draw bar in a direction in which the collet clamps the tool; a shank to be inserted into the tool spindle; a spindle comprising an axis perpendicular to an axis of the shank; a housing rotatably supporting the shank and the spindle, the housing comprising an internal transmission mechanism configured to transmit drive force of the shank to the spindle; a collet disposed on the spindle and configured to clamp a tool; a draw bar disposed in the spindle to move forward and backward to clamp and unclamp the collet; and a spring mechanism configured to bias the draw bar in a direction in which the collet clamps the tool; the tool unclamping operation device (370, 380) comprising: restriction means (380, 510, 610) for restricting a portion of the angle tool holder (200, 200a, 200b) and for receiving force in an axial direction of the spindle; and a hydraulic piston configured to press the draw bar of the angle tool holder (200, 200a, 200b), restriction means (380, 510, 610) for restricting a portion of the angle tool holder (200, 200a, 200b) and for receiving force in an axial direction of the spindle; and a hydraulic piston configured to press the draw bar of the angle tool holder (200, 200a, 200b), wherein the tool attached to the angle tool holder (200, 200a, 200b) is changed by the tool changer and the tool unclamping operation device, characterized in that the tool unclamping operation device (370, 380) further comprises an angle tool holder rest (360, 500, 600), the restriction means (380, 510, 610) is disposed on the angle tool holder rest (360, 500, 600), and that a point of application of force that the restriction means (380, 510, 610) receives when the hydraulic piston presses the draw bar is one point on a vertical plane within which the axis of the spindle is contained.