An apparatus for carrying out a continuous process for preparing propylene glycols. The function is based on relative changes in the load on the strain gauge from a preset reference thereby allowing use of sensors with low resolution, which thereby are comparatively cheap. By use of the musical instrument ID, the user downloads a program or content item suitable for the electronic musical instrument from a program distribution computer or a contents distribution computer via the network. The degrees of resource reuse are determined based on the interference estimates and are used to derive at least one correction factor. In this case, a first and a second charging circuit each produce a charging voltage and decoupling device decouples the first charging circuit when there is a prescribed ratio between the charging voltage of the second charging circuit and an input voltage for the rectifier circuit. Accordingly, an area occupied by the unit nozzle can be reduced, and ink flow in the ink chamber is easily controlled, thereby enhancing a printing speed and a print quality.