  On a compact Riemannian manifold $M$ with boundary $Y$, we express the log of
the zeta-determinant of the Dirichlet-to-Neumann operator acting on $q$-forms
on $Y$ as the difference of the log of the zeta-determinant of the Laplacian on
$q$-forms on $M$ with absolute boundary conditions and that of the Laplacian
with Dirichlet boundary conditions with some additional terms which are
expressed by curvature tensors. When the dimension of $M$ is $2$ or $3$, we
compute these terms explicitly. We also discuss the value of the zeta function
at zero associated to the Dirichlet-to-Neumann operator by using a conformal
rescaling method. As an application, we recover the result of the conformal
invariance obtained in C. Guillarmou and L. Guillop\'e, The determinant of the
Dirichlet-to-Neumann map for surfaces with boundary, Int. Math. Res. Not. IMRN
2007, no. 22, Art. ID rnm099, when the dimension of $M$ is $2$.
