A mathematical model for the hit phenomenon in entertainment within a society is presented as a stochastic process of interactions of human dynamics. The model uses only the time distribution of advertisement budget as an input, and word-of-mouth (WOM) represented by posts on social network systems is used as data to compare with the calculated results. The unit of time is a day. The calculations for the Japanese motion picture market based on to the mathematical model agree very well with the actual residue distribution in time. The model is applied also to weekly TV drama and electronic consumer goods market.