The article describes the planning and construction of the Physico-Technical Institute cyclotron, the fortieth anniversary of the startup of which was observed in 1986. A review of the principal results of the work of the cyclotron laboratory is given: the production of microquantities of plutonium, the measurement of neutron cross sections, and the results of systematic investigations of the Coulomb excitation of nuclear levels by means of ions accelerated in the cyclotron (from He to Ar) and investigations of highly excited and high-spin states of nuclei with A < 100. Special attention is given to applied studies carried out using the cyclotron--the production of semiconductor devices by means of implantation and the development of new methods of study of the composition of surface layers of solids.