Magnetic properties of the layered itinerant system Sr1-xCaxCo2P2 were investigated under a magnetic field up to 70 T. As for the exchange-enhanced Pauli paramagnetic metal SrCo2P2, the magnetization curve shows two characteristic anomalies. The high-field anomaly corresponds to an itinerant-electron metamagnetic transition (IEMT), while the low-field one is small and broad without any obvious hystereses just as the crossover phenomenon between different energy states. Such a successive transition in the magnetization curve cannot be explained by the conventional phenomenological theory for IEMT based upon the Landau expansion of the magnetic free energy, but by the extended Landau expansion theory dealing with two distinguishable energy states. In the systematical study on Sr1-xCaxCo2P2, furthermore, the metamagnetic transition field decreases and goes to zero as x increases up to 0.5, indicating that the ferromagnetic quantum critical point exists at x similar to 0.5.