An LED unit includes a plate-shaped base; a light-emitting device placed on a surface of the base and having one or more LED chips; and a cover mounted to the base at a location above a front side of the light-emitting device and having a function to transmit light emitted from the light-emitting device. The base has on the surface thereof an annular groove for receiving a seal therein, and the cover has on a surface thereof directed to the base an annular protruding part, the annular protruding part being inserted into the annular groove to seal the base and the cover through the seal. A distance between the protruding part and the groove in a width direction of the groove is shorter in a section of the groove than the other sections of the groove.