A program-executing apparatus has a simple configuration, is capable of executing high-speed processing, and is capable of providing high security. The apparatus is configured such that a host system wherein a program execution environment using a general-purpose OS 16 is set and a subsystem 200 wherein a virtual-machine execution environment is set are built into independent operation circuits, and a DPRAM 3 is coupled to a general-purpose bus that connects the two operation circuits. In one of the systems 100 and 200, when a process to be requested to the other system has occurred, an interface built into each of the systems writes a command indicative of the contents of the process into the DPRAM, and outputs an interrupt to the remote system; and in response to an interrupt notified from the other system, the interface executes a process of reading a command written by the DPRAM 3.