We propose a ref lection-type all-optical switch for ultrashort pulses based on a single asymmetrically confined photonic crystal (PC) defect. By changing the absorption of the defect rather than its refractive index, we obtain modulation of ref lectivity with a large extinction ratio. In addition, the control light can be strongly localized in the defect region and completely absorbed by optimization of the absorption of the defect. More importantly, the significant broadening of the defect mode ensures perfect ref lection of ultrashort pulses. Finite-difference time-domain simulation of the switching operation of a three-dimensional PC structure for a 500-fs optical pulse is performed. Switching energy of a few femtojoules is achieved.