PURPOSE: To obtain a rock wool board whose whole body is colored and can be used as a sound-absorbing board by mixing a rock wool slurry with colored pulp and then making the board from the mixture.

CONSTITUTION: This method for producing a rock wool board comprises dispersing rock wool and a binder in water to prepare a rock wool slurry 1, charging colored pulp into a pulper 6 to disintegrate the colored pulp and disperse, transferring the dispersed colored pulp from the pulper 6 into the rock wool tank 3 to mix the slurry with the colored pulp, feeding the mixture into a board- making vat 4, and making the wet mat 2 from the mixture by the use of a board-making cylinder 5 whose inner pressure is reduced.