A strain wave gearing has a lubricant sealing structure that prevents a lubricant from leaking to the outside through a gap portion between a hollow input shaft and an end plate. The lubricant sealing structure includes an oil-repellent surface formed on the surface portion facing the gap portion, an oil seal that seals the gap portion, and an oil film forming surface formed at a lip tip surface of the oil seal. The oil-repellent surface has a surface texture in which first fine grooves are formed in a predetermined pattern so that an oil-repellent effect can be obtained with respect to the lubricant. The oil film forming surface has a surface texture in which second fine grooves are formed in a predetermined pattern so that an oil film forming effect of a seal lip grease can be obtained.