Integrating real-time and general-purpose operating systems into a single embedded device is promising scheme to support both real-time responsiveness and rich functionality with reasonable engineering cost. However, even if the modification for a single combination of real-time and general-purpose operating systems is small, it would be problematic when considering combinations of various operating systems. It is usual for manufacturers to leverage diverse operating systems, depending on real-time constraint, application set, software property they own, etc. In this paper, we introduce a thin virtualization layer for integrating real-time and general-purpose operating systems with a minimal modification to each operating system kernel. Using our virtualization layer, we integrated TOPPERS RTOS and Linux on the SH-4A processor platform with a few dozen lines of modification to each kernel, while introducing sufficiently-small overhead to both real-time responsiveness and system throughput.