A lateral light-emitting device for connecting a medullary guide wire is disclosed. The device comprises a closed main body, a front-end protecting unit for protecting the front end of the main body, and a connecting unit disposed at the distal end of the main body. The inside of the main body is further arranged with a lighting unit, a power supply unit, a light-scattering unit, a light intensity modulating unit, if necessary, and at least one transparent window. The device is able to fit to different types of medullary guide wires. The power supply unit provides power to the lighting unit to produce light emitted to the light-scattering unit and being diverted laterally through the transparent window of the main body after suitably modulating the light intensity. Thereby, the device is illuminated from within the bone cavity to allow observing the operating screw hole location from outside of the body and to enable precisely nailing while proceeding with the intra-medullary nailing procedure.
