To provide a device for measuring particle size distribution which can rapidly carrying out setting work by improving the operability in the case of utilizing a help function.

The setting screen 25c of the displaying device is provided with a plurality of setting items 42 necessary to measure the particle size distribution, and with help buttons 43 corresponding to these setting items 42, respectively. When the help button 43 is operated, the change into a guiding screen is carried out, and the guidance relative to the setting item corresponding to the operated help button is displayed. In addition, when a specific term in the guidance is selected, the change into a reference screen is carried out, and information relative to the content of term is displayed.