A method for determining channel quality estimates of two or more types of subframes, such as clean and unclean subframes, may be applicable to both legacy and newer user equipment. Each movable arm is formed by a plate member including a first metal plate to be substantially in parallel with a side surface of the head slider. The retainer 16 has outlets 16h adjacent to both ends of the gas generator 20 in a longitudinal direction of the gas generator 20 that is accommodated in the retainer 16.