A shutter mechanism includes a shutter, a shutter support, and an elastic member. The shutter moves in one direction to close an opening. The shutter support supports the shutter. The elastic member biases the shutter and the shutter support in opposite directions. The shutter includes an abutting portion to hook on the shutter support with the abutting portion being biased by the elastic member. At least one of the abutting portion and the shutter support has a hook strengthening structure to strengthen hooking of the shutter on the shutter support.