To spray powder uniformly by a method in which the upper end of an oscillating sieve which is oscillated by an oscillator is suspended by a flexible string, and the lower end is contacted with a flexible wire so that the sieve is slanted at a prescribed angle.

The upper end of an oscillating sieve 9 which is oscillated by an oscillator 9B is suspended from an upper frame 1A by a flexible string of a loop-shaped rubber string or a flexible belt, the lower end of the sieve 9 is contacted with a flexible wire 20 such as a piano wire which is stretched through slide brackets 13 of the right and left side frames 1B of a forming chamber 1, a pair of front and rear long holes is formed in each bracket 13, and the sieve 9 is fixed by bolts and nuts through the holes. In the sieve 9, a suspension ring 19 is slid horizontally, or the bracket 13 is slid horizontally in the hole to adjust an inclination position at a prescribed angle. Thus, powder can be sprayed uniformly to form an inorganic plate with uniform density and strength.