An exoskeleton device for assisting a movement of a metacarpal-phalangeal joint of a hand in a flexion/extension plane r of said joint, said metacarpal-phalangeal joint arranged for carrying out a rotation θ about an axis z substantially orthogonal to said flexion/extension plane, the device comprising: - a metacarpal support arranged to be kept integral to a metacarpal portion of the hand; - a phalangeal support having means for fastening to a proximal phalanx; - a kinematical chain between said metacarpal support and said phalangeal support to provide and carrying out a rotation of said phalangeal support with respect to said metacarpal support; said kinematical chain comprises: - a metacarpal slide arranged to slide with respect to said metacarpal support along a predetermined line γ, said predetermined line γ arranged in said flexion/extension plane Γ; - a stiff link pivotally connected to said metacarpal slide by a first pivotal constraint; characterized in that said kinematical chain further comprises: - a second pivotal constraint arranged to connect pivotally said stiff link to said phalangeal support; - an actuating means for causing a first rotation to said stiff link at said first pivotal constraint, and for causing a second rotation to said phalangeal support at said second pivotal constraint, said actuating means being configured for zeroing constraint forces of said exoskeleton device on said metacarpal-phalangeal joint versus said rotation θ, for any position of said metacarpal-phalangeal joint with respect to said exoskeleton device, within a predetermined range. - a metacarpal support arranged to be kept integral to a metacarpal portion of the hand; - a phalangeal support having means for fastening to a proximal phalanx; - a kinematical chain between said metacarpal support and said phalangeal support to provide and carrying out a rotation of said phalangeal support with respect to said metacarpal support; - a metacarpal slide arranged to slide with respect to said metacarpal support along a predetermined line γ, said predetermined line γ arranged in said flexion/extension plane Γ; - a stiff link pivotally connected to said metacarpal slide by a first pivotal constraint; characterized in that said kinematical chain further comprises: - a second pivotal constraint arranged to connect pivotally said stiff link to said phalangeal support; - an actuating means for causing a first rotation to said stiff link at said first pivotal constraint, and for causing a second rotation to said phalangeal support at said second pivotal constraint, said actuating means being configured for zeroing constraint forces of said exoskeleton device on said metacarpal-phalangeal joint versus said rotation θ, for any position of said metacarpal-phalangeal joint with respect to said exoskeleton device, within a predetermined range. - a second pivotal constraint arranged to connect pivotally said stiff link to said phalangeal support; - an actuating means for causing a first rotation to said stiff link at said first pivotal constraint, and for causing a second rotation to said phalangeal support at said second pivotal constraint, said actuating means being configured for zeroing constraint forces of said exoskeleton device on said metacarpal-phalangeal joint versus said rotation θ, for any position of said metacarpal-phalangeal joint with respect to said exoskeleton device, within a predetermined range.