A system comprising: an information processing device; and an external storage device for storing information received from the information processing device, the information processing device including: a first storage unit; a first generation unit for performing a conversion of target information to be stored in the external storage device using a secret sharing scheme in which predetermined reference number pieces of divided data are required to restore the target information, so as to generate multiple pieces of divided data whose number is larger than the reference number; an output unit for selecting first number pieces of divided data from among the generated multiple pieces of divided data, the first number being equal to or larger than the reference number, and outputting the selected first number pieces of divided data to the external storage device; a first storage execution unit for storing second number pieces of divided data except for the outputted first number pieces of divided data among the generated multiple pieces of divided data, in the first storage unit, and the external storage device including: a second storage unit; a second storage execution unit for storing each of the first number pieces of divided data inputted from the information processing device, in the second storage unit; and a data destruction unit for destroying a number of pieces of divided data stored in the second storage unit wherein the number is larger than the difference between the reference number and the first number and equal to or smaller than the sum of the difference and the second number, among the stored first number pieces of divided data if a predetermined reference time has elapsed since a time point of receipt of a predetermined operation. an information processing device; and an external storage device for storing information received from the information processing device, the information processing device including: a first storage unit; a first generation unit for performing a conversion of target information to be stored in the external storage device using a secret sharing scheme in which predetermined reference number pieces of divided data are required to restore the target information, so as to generate multiple pieces of divided data whose number is larger than the reference number; an output unit for selecting first number pieces of divided data from among the generated multiple pieces of divided data, the first number being equal to or larger than the reference number, and outputting the selected first number pieces of divided data to the external storage device; a first storage execution unit for storing second number pieces of divided data except for the outputted first number pieces of divided data among the generated multiple pieces of divided data, in the first storage unit, and a first storage unit; a first generation unit for performing a conversion of target information to be stored in the external storage device using a secret sharing scheme in which predetermined reference number pieces of divided data are required to restore the target information, so as to generate multiple pieces of divided data whose number is larger than the reference number; an output unit for selecting first number pieces of divided data from among the generated multiple pieces of divided data, the first number being equal to or larger than the reference number, and outputting the selected first number pieces of divided data to the external storage device; a first storage execution unit for storing second number pieces of divided data except for the outputted first number pieces of divided data among the generated multiple pieces of divided data, in the first storage unit, and the external storage device including: a second storage unit; a second storage execution unit for storing each of the first number pieces of divided data inputted from the information processing device, in the second storage unit; and a data destruction unit for destroying a number of pieces of divided data stored in the second storage unit wherein the number is larger than the difference between the reference number and the first number and equal to or smaller than the sum of the difference and the second number, among the stored first number pieces of divided data if a predetermined reference time has elapsed since a time point of receipt of a predetermined operation. a second storage unit; a second storage execution unit for storing each of the first number pieces of divided data inputted from the information processing device, in the second storage unit; and a data destruction unit for destroying a number of pieces of divided data stored in the second storage unit wherein the number is larger than the difference between the reference number and the first number and equal to or smaller than the sum of the difference and the second number, among the stored first number pieces of divided data if a predetermined reference time has elapsed since a time point of receipt of a predetermined operation.