A backlight module includes a light guide plate and a light emitting unit. The light guide plate has a first side surface, a second side surface, and a third side surface. The first side surface is located opposite to the second side surface. A height of the first side surface is greater than a height of the second side surface. The third side surface is located between the first side surface and the second side surface and has a light entrance surface and a light exit surface. The light entrance surface is connected to the first side surface and the light exit surface. The light exit surface is connected to the second side surface. An included angle is formed between the light entrance surface and the light exit surface. The light emitting unit is disposed on the light entrance surface.