  We consider a quantum cosmology with a massless background scalar field $\pb$
and adopt a wave packet as the wave function. This wave packet is a
superposition of the WKB form wave functions, each of which has a definite
momentum of the scalar field $\pb$. In this model it is shown that to trace the
formalism of the WKB time is seriously difficult without introducing a complex
value for a time. We define a semiclassical real time variable $\tp$ from the
phase of the wave packet and calculate it explicitly. We find that, when a
quantum matter field $\pq$ is coupled to the system, an approximate
Schr\"odinger equation for $\pq$ holds with respect to $\tp$ in a region where
the size $a$ of the universe is large and $|\pb|$ is small.
