The present invention relates to a flashlight for long time use. Specifically, the flashlight for long time use has a zoom function for adjusting an area shone by light to send the light to a long distance and may be variously used for the military and the leisure, etc. by protecting a PCB from heat generated in a battery contact point and an LED. The flashlight of the present invention comprises a case including a vertical part having a battery containing hole for containing a battery therein, a horizontal part which is vertically extended from one end of the vertical part, and a thermal barrier wall located between the vertical part and the horizontal part; a light emitting body which has one end contained in the horizontal part and having a printed circuit board and the other end to which an LED is inserted and which has the length of at least 1.5Cm or more; a zoom adjusting body which contains the light emitting body and has one end coupled to a terminal of the horizontal part to be slid forward and backward along the horizontal part or to be rotated moved using conchoids; a convex lens which is inserted into the zoom adjusting body to be located in the front of the LED; and a lens cover which is coupled to one end of the zoom adjusting body to fix the convex lens.