To provide a speed reduction gear mechanism which has a high reduction ratio and is capable of preventing the influence of foreign matter such as sand.

A speed reduction gear 44 is constituted of an input side gear 44a engaged with a one-tooth gear 40 provided integrally with a winding knob 13 and an output side gear 44b engaged with a winding completion display plate 42. The pitch circle diameter and tooth phase of the output side gear 44b are made the same as those of the input side gear 44a and a tooth-lacked part 44c without a tooth is provided. Thus, the reduction ratio between the output side gear 44b and the winding completion display plate 42 can be made high and further, even if the foreign matter such as the sand rides on the input side gear 44a, the foreign matter is never bitten into the gap between the output side gear 44b and the winding completion display plate 42.