PURPOSE: To set an image pickup magnification of the CRT measurement device automatically to a proper magnification with high accuracy.

CONSTITUTION: A CCD 17 picks up a measurement pattern image displayed on a CRT 1 at the start of measurement and picture data are stored in a picture memory circuit 6. An arithmetic operation control circuit 7 calculates an arrangement pitch of a phosphor image in an arrangement pitch calculation region having a larger light emitting region than a prescribed measurement region in the lateral direction from the picture data and applies a prescribed correction to the distortion aberration of a pickup lens system 12 to the arrangement pitch to calculate the arrangement pitch of the phosphor image in the measurement region. Furthermore, a current pickup magnification βO of the image pickup lens system 12 is calculated from the arrangement pitch of the phosphor image in the measurement region and a zoom motor 15 is subject to drive control through a zoom motor drive circuit 16 based on a deviation between the pickup magnification βO and a proper magnification βR thereby setting automatically the image pickup lens system 12 to the proper magnification βR.