To provide a portable information display device which can prevent an improper outflow of internally-stored information, for example, in the case where the device is left behind.

The device comprises a main body part 1 having a display part 2, an operating part 3 and internal information storing part 6a and, in addition, a security key 10 which can be attached to/detached from an attachment part 4a of the main body part 1. The security key 10 has a data transmitting part 15. Predetermined data are transmitted from the data transmitting part 15 to a data receiving part 7 of the main body part 1 in the state where the security key 10 is being attached to the security key attachment part 4a. Receipt of the predetermined data from the security key 10 enables execution of predetermined operations about the internally-stored information. In the state where the security key 10 is not attached, the predetermined operations do not start to be executed even when the attachment part 3 of the main body part 1 is operated.