A controller (portable electronic apparatus) includes a housing and a key provided for protruding and retreating movement on the housing. The housing has a front face, a rear face, and a side face for connecting the front face and the rear face to each other. The key has a body having one end inserted in an opening formed in the side face and the other end exposed to the outside of the housing, and an extension extending along the side face from the other end of the body to the outside farther than an end edge of the opening. With the controller (portable electronic apparatus), the area of the face of the key which is exposed to the outside of the housing, that is, the area of the face which opposes to a finger of a user, can be increased. Therefore, at whichever position the face is depressed, the key can be inputted and the contact area with the finger can be increased.