Disclosed are a locking device and an assembly of conjugated electric connectors equipped with the locking device. The device includes: at least one latch presenting a first locking relief, at least one bolt that can be inserted into the latch, and a flexible tongue received in a casing of the bold, the tongue being provided with a second locking relief forming a fitting with the first locking relief. Application includes the implementation of connectors and in particular of high-power connectors for vehicles and electric pieces of equipment.