An electromechanical brake system comprising: a brake disk ; a pair of first and second brake pads (7 and 6) axially opposed to each other with the brake disk disposed therebetween; a linear motion mechanism including a rotary shaft configured to be rotated by an electric motor , and a tubular outer ring member , the linear motion mechanism being configured such that, when the rotary shaft is rotated by the electric motor , rotation of the rotary shaft is converted to a linear motion of the outer ring member , and the first brake pad is pressed against the brake disk; a caliper body straddling an outer peripheral portion of the brake disk , and including, at a first end thereof, a claw axially supporting the second brake pad ; a housing for the linear motion mechanism in which component parts of the linear motion mechanism are received in an assembled state, the housing being disposed at a second end of the caliper body opposite from the first end of the caliper body ; a shrinkable boot closing an opening of the housing at an end of the housing opposed to the brake disk ; a support ring fitted to an outer periphery of the outer ring member at a first end of the outer ring member , the support ring being mechanically fastened to the housing while abutting an open end surface of the housing , wherein the boot has a first end coupled to the outer periphery of the outer ring member at the first end of the outer ring member , and a second end coupled to the support ring , wherein said open end surface of the housing faces the brake disk , characterized in that the electromechanical brake system further comprises at least one seal ring providing a seal between the open end surface of the housing and an abutment surface of the support ring abutting the open end surface of the housing , and between an inner periphery of the housing at an end of the housing facing the brake disk and a sliding surface of the outer ring member that is in sliding contact with the inner periphery of the housing . a brake disk ; a pair of first and second brake pads (7 and 6) axially opposed to each other with the brake disk disposed therebetween; a linear motion mechanism including a rotary shaft configured to be rotated by an electric motor , and a tubular outer ring member , the linear motion mechanism being configured such that, when the rotary shaft is rotated by the electric motor , rotation of the rotary shaft is converted to a linear motion of the outer ring member , and the first brake pad is pressed against the brake disk; a caliper body straddling an outer peripheral portion of the brake disk , and including, at a first end thereof, a claw axially supporting the second brake pad ; a housing for the linear motion mechanism in which component parts of the linear motion mechanism are received in an assembled state, the housing being disposed at a second end of the caliper body opposite from the first end of the caliper body ; a shrinkable boot closing an opening of the housing at an end of the housing opposed to the brake disk ; a support ring fitted to an outer periphery of the outer ring member at a first end of the outer ring member , the support ring being mechanically fastened to the housing while abutting an open end surface of the housing , wherein the boot has a first end coupled to the outer periphery of the outer ring member at the first end of the outer ring member , and a second end coupled to the support ring , wherein said open end surface of the housing faces the brake disk , characterized in that the electromechanical brake system further comprises at least one seal ring providing a seal between the open end surface of the housing and an abutment surface of the support ring abutting the open end surface of the housing , and between an inner periphery of the housing at an end of the housing facing the brake disk and a sliding surface of the outer ring member that is in sliding contact with the inner periphery of the housing . <EOS>