Maruyama Seisakusho (丸山製作所) was a Japanese company, known from an advertisement dated January 1944 formerly reproduced at Gochamaze (archived). Its address was Honjo Koume 3–21 in Tokyo (東京・本所・小梅・三の二十一). It was making rollfilm holders for plate cameras, in two types, called マーツ (mātsu) in katakana (the equivalent Roman name is unknown). The large model takes 6×6cm exposures on 120 film and attaches on daimeishi-size (6.5×9cm) cameras; its price was ¥32. The small model takes ten exposures on 127 film, certainly in 4×5cm format, and fits on atom-size (4.5×6cm) plate cameras; it was priced was ¥37. The advertisement says that the mechanism was patented. The company was also offering camera repairs and modifications.
It is completely unknown if the company is related to the manufacturer of gardening tools Maruyama Seisakusho, founded in 1895 and established under that name in 1937.