The IJAAF and the IJNAF used these wagons to carry around their heavier bombs. But they were mostly found in the bigger airfields of the homeland like the ones in the NARA photos below.
Found after the end of the War at the seaplane base in Otsu, capital of Shiga prefecture, next to lake Biwa, the biggest lake in Japan. The bottles in the foreground on the left wrapped with paper are somewhat of a mystery. Occasionally sake bottles are wrapped with paper like that but no idea what they are doing next to floatplanes and bomb wagons. *
This photo was taken in Atsugi, Kanagawa Prefecture. Note the quite large bombs, probably 250kgs, and the concrete airplane shelters in the background.
*And now for the language/culture lesson of the day. In Japanese the word sake (pronounced "SA"-as in "SAmantha" and KE-as in "KEvin"; not as in "key") and osake (with the honorific "o") means any kind of alcoholic drink (whiskey, vodka etc). The word the Japanese use for the drink known to the Western World as sake, is nihonshu. Enjoy your sushi or sashimi with cold or hot nihonshu.
My personal favorite is hirezake which Wikipedia describes as: The fins of the fish [Fugu or pufferfish: the well-known poisonous fish] are dried out completely, baked, and served in hot sake.