These are revenue stamps issued by a traders union of grain sacks (bags) in Chiba prefecture, it looks.
The postmark was the first clue to find out the area of issue, as the Chosei District is still existing. https://en.wikipedia.org/wiki/Ch#333;sei_District
Second clue was the background pattern, which looks straw mat for living floor. Then the old character of Kamasu is found, that means straw made bags/sacks.
Letters in the stamp are written from right to left - before 1947 manner. But the postmark is made left-to-right modern way. So, they were printed before 1947 and used after, I guess. No further identification, as I don't have relevant catalogue. Even this link below, list of non-govermental revenue stamps doesn't have this one.https://muuseo.com/carow151852/collection_rooms/6