  We report magnetic properties of the layered itinerant system,
Sr$_{1-x}$Ca$_x$Co$_2$P$_2$ in the magnetic field up to 70 T. As for the
exchange-enhanced Pauli paramagnetic metal SrCo$_2$P$_2$, the magnetization
curve shows two characteristic anomalies. The low-field anomaly is small
without obvious hysteresis, and the high-field one is a typical behavior of the
itinerant-electron metamagnetic transition (IEMT). Such a successive transition
in the magnetization curve cannot be explained by the conventional
phenomenological theory for IEMT due to the Landau expansion of the free
energy, but by the extended Landau expansion theory with distinguishable two
energy states. In the systematical study of Sr$_{1-x}$Ca$_x$Co$_2$P$_2$,
furthermore, the metamagnetic transition field decreases and goes to zero as
$x$ increases up to 0.5, indicating that the ferromagnetic quantum critical
point (QCP) exists at $x \sim 0.5$.
