Working head for working pieces, comprising: - a motion transmission group comprising a shaft having a longitudinal axis and a motor for rotating said shaft about said longitudinal axis, - a plurality of tools (T 1, T 2...T N), - a plurality of spindles (M 1, M 2...M N) having a respective longitudinal axis (A 1, A 2...A N), wherein each spindle (M 1, M 2...M N) comprises a first end portion shaped to support a respective tool (T 1, T 2...T N) and movable between a rest position, in which a respective first end portion is at least partially retracted into said working head, and an operating position, in which a respective first end portion is translated of a predetermined distance along the respective longitudinal axis (A 1,A 2...A N) of the spindle (M 1, M 2...M N), - a motion transmission mechanism (CR, R 1, R 2...R N) to transmit the rotary motion of the shaft of said motion transmission group to each spindle (M 1, M 2...M N), wherein said working head comprises a respective coupling device (G1,G2) for each spindle (M 1, M 2...M N) to couple a spindle (M 1, M 2...M N) to said motion transmission mechanism (CR, R 1, R 2...R N) when said spindle (M 1, M 2...M N) is in operating position, in such a way that a rotatory motion is transmitted by said motion transmission group to said spindle (M 1,M 2...M N), and to uncouple a spindle (M 1,M 2...M N) from said motion transmission mechanism (CR, R 1, R 2...R N) when said spindle (M 1, M 2...M N) is in rest position, in such a way that a rotary motion of said motion transmission group is not transmitted to said spindle (M 1, M 2...M N), wherein each coupling device (G1,G2) comprises first releasable coupling means integral with said motion transmission mechanism (R 1, R 2...R N), and second releasable coupling means for each spindle (M 1, M 2...M N), wherein said second releasable coupling means are integral with a respective spindle (M 1, M 2...M N) and are configured to be coupled/uncoupled to/from respective first releasable coupling means in such a way that one or more spindles (M 1, M 2...M N) are in operating position only when said first releasable coupling means (G1; L1) are coupled to respective second releasable coupling means, characterized in that said first releasable coupling means consists of at least one first magnet, and said second releasable coupling means consists of at least one second magnet, so that, when said first magnet is coupled to said second magnet, a force of attraction is generated. - a motion transmission group comprising a shaft having a longitudinal axis and a motor for rotating said shaft about said longitudinal axis, - a plurality of tools (T 1, T 2...T N), - a plurality of spindles (M 1, M 2...M N) having a respective longitudinal axis (A 1, A 2...A N), wherein each spindle (M 1, M 2...M N) comprises a first end portion shaped to support a respective tool (T 1, T 2...T N) and movable between a rest position, in which a respective first end portion is at least partially retracted into said working head, and an operating position, in which a respective first end portion is translated of a predetermined distance along the respective longitudinal axis (A 1,A 2...A N) of the spindle (M 1, M 2...M N), - a motion transmission mechanism (CR, R 1, R 2...R N) to transmit the rotary motion of the shaft of said motion transmission group to each spindle (M 1, M 2...M N), said working head comprises a respective coupling device (G1,G2) for each spindle (M 1, M 2...M N) to couple a spindle (M 1, M 2...M N) to said motion transmission mechanism (CR, R 1, R 2...R N) when said spindle (M 1, M 2...M N) is in operating position, in such a way that a rotatory motion is transmitted by said motion transmission group to said spindle (M 1,M 2...M N), and to uncouple a spindle (M 1,M 2...M N) from said motion transmission mechanism (CR, R 1, R 2...R N) when said spindle (M 1, M 2...M N) is in rest position, in such a way that a rotary motion of said motion transmission group is not transmitted to said spindle (M 1, M 2...M N), wherein each coupling device (G1,G2) comprises first releasable coupling means integral with said motion transmission mechanism (R 1, R 2...R N), and second releasable coupling means for each spindle (M 1, M 2...M N), wherein said second releasable coupling means are integral with a respective spindle (M 1, M 2...M N) and are configured to be coupled/uncoupled to/from respective first releasable coupling means in such a way that one or more spindles (M 1, M 2...M N) are in operating position only when said first releasable coupling means (G1; L1) are coupled to respective second releasable coupling means, characterized in that said first releasable coupling means consists of at least one first magnet, and said second releasable coupling means consists of at least one second magnet, so that, when said first magnet is coupled to said second magnet, a force of attraction is generated.