I thought that they were Japanese chestnuts at first but they have no burs. They're Japanese horse chestnuts (Aesculus turbinata). Japanese horse chestnuts resemble European horse chestnuts and Japanese chestnuts very much but Japanese chestnuts open when ripe whereas the Japanese and European horse chestnuts do not. Also, while Japanese chestnuts are edible and sweet, Japanese horse chestnuts are edible but very bitter and the European ones are poisonous. You cannot mistake one for another...
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| Japanese horse chestnut (Aesculus turbinata) トチノキ（栃の木） |
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| The horse chestnut bur does not open even when ripe 熟しても栃の木の蒴果は閉じたまま |
