To enhance visibility of a warning sign for a railroad crossing alarm in a night time.

This a warning-sign for a railroad crossing alarm comprises an X-mark partitioned into a black-colored area 9 and an yellow-colored area 10 to be classified by color. The warning sign has a surface light-emitter 11 and a light-emitting source 12. The emitter 11 forms the yellow area 10, and a light guide panel is used therefor. The light guide panel emits from a surface direction the light of the source 12 incident from an end face so as to make its surface luminous, has light transmissivety, and is superposed on a colored sheet 14 to be arranged. The source 12 is an yellow-color light-emitting LED for making the emitter 11 surface-luminous. In a night time, light emitted from the LED gets incident into the emitter 11 to make surface-luminous uniformly the whole surface of the emitter 11, so as to clearly display a shape of the X-mark and stripe pattern comprising the black and yellow colors of the warning sign. When the emitter 11 is not under a luminous condition, a ground color of the yellow-colored area 10 is formed by the light through the light guide panel.