1. A portable information terminal device comprising: an imaging unit for photographing an object; photographing control means for controlling photographing operation performed by said imaging unit; characteristic information storage means for storing characteristic information extracted from face images as registered characteristic information in advance; authentication processing means for performing an authentication process by using said registered characteristic information on a basis of an image photographed by said imaging unit; operation input means that allows a user to select one of a different set of items displayed in a screen on a basis of each user's selection operation of a series of user's selection operations including a last operation that triggers initiation of said authentication process; imaging unit starting means for executing an initialization process of said imaging unit by supplying a power source to said imaging unit on a basis of said user's selection operation prior to said last operation in said series of said user's selection operations; and imaging unit stopping means for stopping said power source to said imaging unit when said user's selection operation different from said last operation in said series of said user's selection operations is carried out after starting said imaging unit, wherein said photographing control means starts photographing on a basis of completion of said initialization process of said imaging unit by said imaging unit starting means, and said authentication processing means starts said authentication process on a basis of said last operation.