Let F (t, x, u, v) be a holomorphic function in a neighborhood of the origin of C 4 satisfying F (0, x, 0, 0) ≡ 0 and (∂F /∂v)(0, x, 0, 0) ≡ 0; then the equation (A) t∂u/∂t = F (t, x, u, ∂u/∂x) is called a partial differential equation of Briot-Bouquet type with respect to t, and the function λ(x) = (∂F /∂u)(0, x, 0, 0) is called the characteristic exponent. In [15], it is proved that if λ(0) ∈ (−∞, 0] ∪ {1, 2, . . .} holds the equation (A) is reduced to the simple form (B 1 ) t∂w/∂t = λ(x)w. The present paper considers the case λ(0) = K ∈ {1, 2, . . .} and proves the following result: if λ(0) = K ∈ {1, 2, . . .} holds the equation (A) is reduced to the form (B 2 ) t∂w/∂t = λ(x)w + γ (x)t K for some holomorphic function γ (x). The reduction is done by considering the coupling of two equations (A) and (B 2 ), and by solving their coupling equations. The result is applied to the problem of finding all the holomorphic and singular solutions of (A).