The objective of this study is to estimate the social cost of agricultural machinery accidents by using the Gross Lost Output Approach, considered to be well-suited method. The number of 118 accidents were used for the estimation of the social cost of agricultural machinery accidents. Agricultural machinery accidents on this study includes only the accidents of power-tiller, tractor, transplanter, combine and small-managerial power-tiller. First of all, the social cost of one accident in agricultural machinery was estimated as 97.7～97.8 million won that is 4 fold of farm household income. Direct cost(future income loss + medical cost + vehicles repairing cost) of the agricultural machinery accidents was over 1.7 fold of farm household income. The largest cost of accident was happened in tractor accident, was estimated 128.6 million won.