PURPOSE: To provide a method and device for lighting a low pressure mercury lamp and an ultraviolet irradiating device using this lamp capable of improving efficiency in the case of high frequency lighting the low pressure mercury lamp.

CONSTITUTION: An electrode 4 is sealed in both ends of an arc tube 2 constituted of quartz glass, and the inside of the arc tube 2 is sealed with mercury and rare gas. In this low pressure mercury lamp 1, in the case of assuming 3A or more for lamp current, 1Torr or less for seal pressure of rare gas, P (Torr) for seal pressure of this rare gas and Dmm for lamp internal diameter, the lamp 1 is lighted by a high frequency of 50kHz or more under a condition of P×D≤35. Accordingly, since the lamp is lighted by the high frequency of 50kHz or more, an electron temperature is increased to improve the efficiency.