Oscillations of the magnetic field in sunspot umbra have been detected by Pulkovo CCD spectroheliograph-magnetograph. The manifestations of 3- min oscillations in the power spectra of magnetic field variations are not very strong and can be seen only in a number of larger sunspots. Their power is concentrated in isolated small regions of the boundary between umbra and penumbre of large spots. The waves are produced in short bursts with coherence times of about 10 min. In the sunspot umbra, 30-40 min modes have been also confidently revealed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html