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 (61, 63, 69, 71) 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 (61, 63, 69, 71) 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.