To simplify structure as the whole device and facilitate locking- unlocking operation by constituting the valve lock device in such a way that an unlock cutout of each tumbler occupies a position of being adjusted opposedly to a fitting insert part of a locking member to release constraint of the locking member at the time of unlocking with key cards inserted in key holes.

In case of opening valves provided every liquid tank of a tank lorry, two key cards, duplicate keys, are inserted in key holes 43, 44 in the direction of arrow marks P so as to oscillate two tumbler groups 5a, 5b from a lock position to an unlock position against a tumbler spring 53 or the like. Unlock cutouts 52 of all tumblers 5 are thereby adjusted opposed to a fitting insert part 67 of a locking member 6, and then an operating part piece is gripped to displace the locking member 6, released from constraint, frontward. Then engagement between the locking member 6 and a locking plate 2 is released, so that a rotatory-operating shaft 12 becomes free to rotate, and the operating shaft 12 is turned by a handle 13 to open a valve. In this lock device, the valve cannot be opened/closed unless using two key cards.