EN
We will consider the nonlinear partial differential equation <br> $t^{γ}(∂/∂t)^{m}u = F(t,x,{(∂/∂t)^{j}(∂/∂x)^{α}u}_{j+|α|≤L,j<m})$ (E) <br>(with γ ≥ 0 and 1 ≤ m ≤ L) and show the following two results: (1) (Maillet type theorem) if (E) has a formal solution it is in some formal Gevrey class, and (2) (Gevrey regularity in time) if (E) has a solution $u(t,x) ∈ C^{∞}([0,T],𝓔^{σ}(V))$ it is in some Gevrey class also with respect to the time variable t. It will be explained that the mechanism of these two results are quite similar, but still there appears some difference between them which is very interesting to the author.