First of all, sorry for slow response to the subject.
I had built whole my NetBSD before I tried.

I've copied the related header files to /usr/include/g++
with the way as Tom Ivar Helbekkmo said.
 Just adding a section to /usr/src/gnu/lib/libg++/Makefile
as follows:

        @echo installing includes from libio
        @(cd libio ; for j in *.h; do \
                cmp -s $$j ${DESTDIR}/usr/include/g++/$$j || \
                install -c -o ${BINOWN} -g ${BINGRP} -m 444 $$j \
                        ${DESTDIR}/usr/include/g++/$$j; \
        done)

and 'make includes' in the directory.

After that, linking a C++ program with "-ltermcap" fixes the
problem.

It may works fine, though we still do not know why.

Anyway, thanks for your help.

--
Tatsuaki Wada
       Dept. Electrical and Electronic Engineering
       Ibaraki University
       4-12-1 Nakanarusawa, Hitachi, 316, Japan.
e-mail:  wada@ee.ibaraki.ac.jp