To provide a blade fixing device for a saw not only simply structured, securing low cost and a low rate of failure, but also simply and quickly removing or assembling the blade.

When the blade is mounted, a brake knob is pushed and a slide part is moved from the first position to the second position, and a deeper part of the braking surface of a brake tank is positioned at the second opening of a through hole, which causes the base part of the blade to intrude into an installation tank, and a sphere is moved by the base part to the brake tank along the through hole and intruded into the brake tank. When the base part of the blade reaches the prescribed position, the slide part is restored to the second position by the tension of a resilient unit if one separate his hand from the brake knob, and the braking surface moves the sphere to a bored hole near the base part of the blade to cause running against the wall of the installation tank. Because the sphere intrudes into the bored hole, the blade is fixed without separating from a blade fixing device. When removed from the blade fixing device, the blade is taken out by pushing again the brake knob.