wherein an [x] represents encrypted data of an x,

processing circuitry configured to

sort by [Time Information] and then sort by [User ID] an encrypted data set group including a plurality of encrypted data sets, each of the plurality of encrypted data sets including a [Location ID], the [User ID], and the [Time Information] obtained by having encrypted analysis target data of an analysis target data set of a Location ID, a User ID, and Time Information respectively by another device, wherein the analytical target data of the analysis target data set represents unencrypted data that indicate a certain user stays at a certain location at certain time;

generate a [Flow] by extracting the [Location ID] according to the number of hops in a sorted order, the number of hops corresponding to the number of transitions between preset locations, and by further encoding the extracted [Location ID], wherein the [Flow] represents encoded flow information that is generated by without decrypting the encrypted data set group;

storing the [Flow] in a memory device;

determine whether a [User ID] and another [User ID] adjacent to each other are equal, and when not equal, replace a corresponding [Flow] with a [predetermined value that represents invalid] in the memory device;

modifying the [Flow] stored in the memory device as valid data by deleting the [predetermined value that represents invalid] from the [Flow].