The aim of this work is to increase the efficiency of muon track reconstruction and estimate a number of electromagnetic secondaries in the muon detector for experimental data from the Integrated Test set-up, the prototype of CMS endcap segment. The experimental data have shown that the high energy beam of muons (100-300 GeV) produces 20-25% of events with electromagnetic secondaries. Though the muon coordinate measurements were distorted by secondaries, we have managed to obtain a high efficiency (>or=92%) of muon track reconstruction. The investigation has been performed at the Laboratory of Computing Techniques and Automation and the Laboratory of Particle Physics. (4 refs)