In a print system comprised of a printer connected to a plurality of personal computers, the personal computer to which a lock command is inputted by a user outputs an ID code of the personal computer and a lock signal to the printer. The printer memorizes the ID code of the personal computer into a memory and goes into unprintable state. When, a lock release command is inputted to the personal computer, it outputs the ID code and a lock release signal to the printer. When the received ID code coincides with the ID code memorized in the memory, the printer goes into printable state and accepts an image data outputted from the personal computer and perform printing operation with using the image data. Thus, by the simple operation of rejecting acceptance of a print command outputted from another user, it can prevent that the image is printed on an undesirable recording paper sheet for the user.