Recycling of printed circuit boards (PCBs) is an important subject not only from the treatment of waste but also from the recovery of valuable materials including rare metals. We have tried a special and selective grinding such as parts detachment from the board using drum typed agitation mill to concentrate a part of "rare metals". The objective of this study is revealing the mechanism of parts detachment process from PCBs. A simulant PCBs on which nine capacitors were solder-mounted were used for the communition test using the agitation mill. Effects of rotation speed and the number of boards for parts detachment or board breakage were investigated. Both of parts detachment rate and board breakage rate were increased as rotation speed increased. On the other hand, as the number of boards increased, parts detachment rate was increased while board breakage rate was slightly increased.DEM simulation with and without particle breakage model was conducted. DEM simulation with spherical particle model (without particle breakage model) showed that board breakage was strongly affected by collision of PCBs to the wall in the normal direction while parts detachment was affected by both of collision of PCBs to the wall in the tangential direction and interaction between PCBs. To investigate the mechanism of parts detachment process more directly, DEM simulation with particle breakage model was also conducted. Simulation results obtained from DEM with particle breakage model corresponded to these experimental trends successfully.