A function that keeps the execution speed of a process constant despite the operation of other processes improves computer operational convenience. In this paper, we have described an I/O performance regulating function, which regulates execution time of a process’s I/O request (I/O time) according to the performance level that has been specified. Specifically, the proposed function limits the number of I/O requests for an I/O device, in order to guarantee that the I/O response time of the target process will achieve a specified time. Furthermore, the proposed function delays waking up the process until the time corresponding to the specified performance, in order to regulate the I/O time of the process. Regarding the usage form on the computer, borrowing virtual machines is widespread, and in this paper, we show that the proposed function can regulate the process I/O time on a virtual machine with high accuracy. In practice, the introduced function cannot regulate the timing of individual I/O actions particularly well, because the I/O time on the virtual machine is too short; however, the function can regulate with high accuracy over a longer term by carrying forward the deviations from each individual regulating events.