1. A computer readable medium storing a program for estimating a user activity from an article to which an article identifier for identification of the article is attached, the program executing instructions to perform the steps comprising: extracting a noun and a verb in a sentence from document data that have been input; calculating a conditional probability of the verb to the noun in accordance with P (verb v|noun n)∝1/(a number of types of verbs)P(noun n|verb v); storing an article identifier and in association with article information corresponding to the noun; storing probability information in association with the noun and the verb that have been extracted, the conditional probability that has been calculated, and the number of the types of the verbs; detecting an article identifier; and estimating the user activity based on the probability information, in response to detection of the article identifier; wherein when a plurality of the verbs are associated with the noun, a plurality of the conditional probabilities of the plurality of the verbs are compared with each other, the estimating step estimates that there is a higher possibility that the user will perform the user activity corresponding to the verb having a higher conditional probability.