The present invention relates to novel podophyllotoxin derivatives substituted in the 4-position by a substituted aminoalkylaminoacetamide chain, to their process of preparation and to their use as medicament as anticancer agents. The front panel and the rear panel confront each other, and peripheries thereof are sealed to form a discharge space therebetween. In this manner, flow is redirected about the elbow of the draft tube. The X-ray imaging apparatus also includes a control means for controlling the X-ray generation means and the AEC detector, where the control means controls the X-ray generation means based on the signal output from the AEC detector, and where the control means controls the AEC detector using correction data to correct an exposure detection element forming a part of the AEC detector.