To provide a readily producible, easily installed and inexpensive artificial sea grass device.

This device is composed by including a pair of leaflike materials 1 composed of a reticulate bag 2 having a bent part 2a arranged in the central part and both closed ends, a stringy artificial sea grass material 4 inserted into each of both sides of the reticulate bag 2 and a float 5 and a holding piece 12 having a cylindrical part 12a holding the bent part 2a in cooperation with a holding rod 10 and an engaging part 12b for engaging with an engaging rod 14 formed under the cylindrical part 12a and arranged in water in the artificial sea grass device A1 engaged with an engaging device 14 fixed in water and used for rearing natural sea grass and seaweed, etc. in water.