NOVELTY - The component unit (10) has a connecting terminal (17) mounted on a circuit board (13). A battery holder (12) holds a battery connected to the connecting terminal of the circuit board. A holder cover (11) covers two sides of the circuit board with the battery holder. Two engaging parts (17a, 17b) are formed in the connecting terminal, and engage the battery holder and the holder cover. A pair of rib shaped terminal introducing parts (11A) is mutually and protrudingly provided in parallel at two sides of a pair of rectangular windows (11a) of an inner surface of the holder cover.    USE - Electronic component unit for use as a portable transmitting apparatus (claimed) i.e. electronic key, in a keyless entry system for locking/unlocking a door of a vehicle.    ADVANTAGE - The engaging parts are formed in the connecting terminal and engage the battery holder and the holder cover, so that the electronic component unit is prevented from being damaged during disassembling. The trace of a fraudulent modification can be identified clearly, thus performing decomposition of the unit without any extra components, and hence reducing production cost of the component unit. The component unit is provided with a sliding prevention part formed in the battery holder, so that the holder cover is prevented from sliding, thus assembling an assembled electronic component unit in an easy manner, and hence improving undestructive property of the component unit. The engaging part is engaged with the sliding prevention part formed in the terminal introducing part, so that sliding of the battery holder and the holder cover can be prevented, thus preventing thermal bad influence exerted on electronic components by heat welding.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a portable transmitting apparatus.    DESCRIPTION OF DRAWING(S) - The drawing shows an exploded perspective view of an electronic component unit.    Electronic component unit (10)    Holder cover (11)    Terminal introducing parts (11A)    Rectangular windows (11a)    Battery holder (12)    Circuit board (13)    Connecting terminal (17)    Engaging parts (17a, 17b)