An information processing system has a main unit, an input device detachable from the main unit, a storage device for storing a startup password set by the input device, a startup password presence checking portion for determining whether or not the startup password is stored, and a startup password request portion for requesting an operator to set a startup password. The startup password request means: (i) requests the setting of the startup password with input unit for starting the main unit, if the input unit is connected to the main unit, and when the startup password is absent, (ii) makes the main unit start, if the input unit is connected to the main unit, and when the startup password is found present, and (iii) makes the main unit start regardless of the presence or absence of the startup password, if the input unit is not connected to the main unit.