An engagement system for removably connecting gardening tools and similar type devices to a power unit comprising a drive motor, the system comprising a base element suitable for being fixed to a crankcase housing the drive motor, a fastening element of a tool that can be actuated by a shaft of the drive motor, suitable for coupling with the base element, a button mounted on the base element and suitable for cooperating with a corresponding opening formed on the fastening element to removably lock the elements in an engagement position, the base element being equipped with at least one electrical safety switch actuated elastically by a rod between a first position in which the electrical safety switch is closed and prevents the operation of the drive motor, and a second position in which the electrical safety switch is open and allows the operation of the drive motor, the second position only being obtainable when the fastening element is engaged with the base element.