To inform the outside of a vehicle of leakage at an informing pattern corresponding to the leakage status of a gaseous fuel when the leakage of the gaseous fuel is generated in the vehicle using the gaseous fuel.

The gaseous fuel leakage informing device 1 is provided with a leakage detection means 12 for detecting the leakage state of the gaseous fuel; a determination part 20 for comparing output of the leakage detection means with a predetermined reference value to determine the gaseous fuel leakage state; and a decision part 22 for deciding the informing pattern of the informing means 18 by output of the determination part 20. The leakage state of the gaseous fuel is detected by the leakage detection means 12, the detected gaseous fuel state is determined by the determination part 20 and the informing pattern of the informing means 18 for informing the outside of the vehicle of it is determined in the decision part 22 based on the determination result.