PURPOSE: To improve the frequency characteristics of beam current detection in a beam current detecting circuit included in a CRT display device.

CONSTITUTION: The output terminal of an image output circuit 5 is connected to the cathod 2 of a CRT 1 through a coupling capacitor 6. In the horizontal scanning period of an image, a clamp pulse generating circuit 11 outputs no pulse and a transistor(TR) 12 is turned off. A luminance signal outputted from the circuit 5 is applied to the cathod 2 and an image is displayed on the CRT 1. At the time, an electron beam current is allowd to flow into the capacitor 6 through a high voltage generating circuit 4, an anode 3 and the cathod 2. In the flyback time of the image, the TR 12 is turned on, the charge of the capacitor 6 is discharged through the 2nd current detector 21. When a difference value between both current detectors 21, 20 is found out, a beam current can be detected without being deteriorated at its frequency characteristics.