Abstract: A lock apparatus of the invention capable of being locked/unlocked by an electronic key, comprises: an electronic key having a circuit chip generating an electronic signal, and an insertion portion provided at an end thereof and comprised of a pair of opposing flat portions and slope portions on both sides so as to be formed in a tapered flat shape; and a rotating member having an insertion hole opening at an end face thereof and in which the insertion portion of the electronic key is to be inserted, an opening portion of the key insertion hole having a rectangular sectional shape corresponding to a cross section of the insertion portion and being larger than an end of the insertion portion, and an interior of the key insertion hole being formed in a tapered flat shape corresponding to the tapered flat shape of the insertion portion and having a slant wall as a side face.