An anti-theft system for construction machines, comprising a memory which stores, as machine-side identification information, first identification information allocated construction machine by construction machine and second identification information allocated in common to plural construction machines, a first collating medium having the same identification information as the first identification information, a second collating medium having the same identification information as the second identification information, a collator which collates the identification information of the first or the second collating medium with the machine-side identification information, and an operation controller which cancels the inhibit of operation of the construction machine concerned when there is obtained a coincident collation result by the collator. With this anti-theft system, an owner of construction machines can manage the construction machines by only one type of a collating medium while preventing theft.