Have you had any storms recently? Wind, rain? That looks more like physiological leaf spot then anything else, which is typically the result of mechanical damage - windburn, hail, heavy rainfall, even brushing by the foliage. As the photos are not clear enough to determine for certain, there could be a little insect damage as well or at any rate, necrosis here and there on the foliage. Uneven watering (allowing the plant to get too dry or watering too heavily) can also result in dried foliage as shown as well. The foliage of Japanese maples is somewhat delicate and can be damaged relatively easily -- even foliar sprays should be avoided to prevent the chance of phytotoxicity.

Bottomline, at this time of year none of the above are serious issues as the plant is about to lose its leaves anyway and enter dormancy. Do check for insects and treat as appropriate. And if in a dry location, make sure the plant is well watered (not over-watered!) through the winter.