Abstract. In our previous work, we established the theory of multi-variable Witten zeta-functions, which are called the zeta-functions of root systems. We have already considered the cases of types A 2 , A 3 , B 2 , B 3 and C 3 . In this paper, we consider the case of G 2 -type. We define certain analogues of Bernoulli polynomials of G 2 -type and study the generating functions of them to determine the coefficients of Witten's volume formulas of G 2 -type. Next, we consider the meromorphic continuation of the zeta-function of G 2 -type and determine its possible singularities. Finally, by using our previous method, we give explicit functional relations for them which include Witten's volume formulas.