In a virtual machine system where a first stage VM and a second stage VM generated on the first stage VM are executed, a processor is configured to perform a first determination as to whether to physically instruct to start execution caused by a virtual execution start of the second stage VM and a second determination as to whether a physical end is detected as a result of a virtual end of the second stage VM, and calculate an execution time of the second stage VM based on results of the first determination and the second determination.