An information processing device for a diver adapted to be used for diving with at least first and second cylinders respectively containing first and second mixed gases in which a plurality of diving gases are mixed with different mixture ratios for each of said first and second cylinders, comprising:
- an oxygen partial pressure calculating and monitoring unit configured to calculate oxygen partial pressure of each of said first and second cylinders,
- said oxygen partial pressure calculating and monitoring unit making automatic switching from said first cylinder to said second cylinder impossible based on a result of calculating said oxygen partial pressure, upon a determination of a possibility of oxygen deficiency or oxygen poisoning in using said second cylinder.