A shutter opening mechanism in a data recording/reproducing device engages a shutter of a disk cartridge which is being inserted into the data recording/reproducing device to open the shutter as the disk cartridge is inserted. The opening mechanism includes a pin and a roller provided at an end of an arm. The pin is formed as a hollow cylinder that includes a slit along a length of the pin, and the roller is provided with a hole. During assembly, the pin is compressed to narrow the slit for insertion into the hole so that the roller is resiliently secured to the pin. Over time, the pin expands and ensures that the roller remains secured to the pin.