To provide a laver acid treatment agent which is rendered a phosphorus-free formulation to prevent an adverse affect on the laver growth environment, and excels in buffer capacity to extremely reduce the variablity of pH, exhibits the acid treatment effect to a maximum, and can surely exterminate miscellaneous algae, bacteria and the like from laver.

Since an organic acid which constitutes mainly the acid treatment agent is mixed with a buffer compound which forms a conjugate base with an acid in a solution and seawater to obtain a state containing a buffer in an acidic solution, the dilution with seawater in the acid treating operation and the variability of pH due to the addition of the acid or a base can be reduced to maintain a necessary acidity for the acid treatment, and thus the acid treatment for laver can be efficiently performed, and there is no need to use a phosphate buffer containing phosphorus which accelerates the eutrophication of seawater, and an adverse affect on the environment surrounding the laver farm can be removed.