I too would be worried about the weed seeds. You can certainly test it by putting some in a pot to water n watch, see what sprouts?

Other ideas are to start another compost pile. Make sure this pile gets hot and add some of this compost as you build it.

Another idea would be to try heating this compost in a gas grill to kill any weed seeds. Tho I would use the pot test above to see IF you will get weeds sprouting?

Are you in fact located in Japan? If so it would probably be advisable to learn about climate and soil variation there. Bear in mind that few if any on this forum will know anything about those very important factors. Local experts are always by far best.

Regarding this specific question, I don't generally worry much about introducing weed seeds because in my gardens pulling weeds is not difficult due to having light soil. So here already soil type is an issue. If your soil is heavy then deep-rooted weeds can be a serious problem. OTOH, it is likely that whatever weeds seeds are in the compost pile are also in the soil of your garden site, and so if your soil is heavy weeds will be a difficult problem regardless until soil fertility and crop rotation is optimum.

Unless you have a particularly nasty weed in there, I wouldn't worry about it. The benefits of that nice black compost is vastly greater than the cost of pulling up a few weeds. Just don't use it to start seedlings, where you could get confused which is which. Unless you use a weed-covering mulch, weeding is just part of gardening. Let 'em come up, and mow 'em down. Your plants will thank for for the compost long after the weeds are gone.

I would use the material you describe as "gorgeous compost" in our garden, or to amend the clay soil around our blueberry shrubs. If any weeds come up, I would simply pull them, and go on gardening.

Hello Japan, from the West coast of the US. :)

Personally I've had both hot and older, long running cold compost piles over the years, and not had weed problems from either, other than the normal amount that just comes with the land, wind and little birds pooping. How is the temperature there now ? Warm I'm guessing. If that's true, I bet if you just pull back the top of the pile and wait a week, you will either see baby weeds popping up, or you won't.

New baby weeds make nice compost. :)

Thanks for the replies, everyone!
I decided to use the compost (my compacted clay soil definitely needs it) and just deal with any weeds that come up while they're small. We'll see how it goes!