In this paper, derivation of equations for the dynamic analysis of closed loop mechanisms is described. The unified method which is applicable to any types of mechanism is obtained as a result. The condition of non-singular matrix which expresses the equilibrium of forces and moments on links and joints shows that the procedure of the derivation is a kind of conventional loop cut method. However, in this method, the forces and moments at cut points can be described by the explicit functions of the forces and moments acting on the links without introducing extra parameters such as the Lagrange's multiplier. It is also shown that the procedure of the derivation can be expressed by linear functions formed by matrices and vectors which helps to develop a computer program with less cost.