A liquid level detection device comprising: a float arm including a float at one end portion thereof; a holder configured to hold the float arm and including a first rotating portion (2b2) and a second rotating portion (2b3); a main body portion including a first rotation support portion configured to rotatably support the first rotating portion (2b2); a cover including a second rotation support portion configured to rotatably support the second rotating portion (2b3); and a detecting portion, wherein, the liquid level detection device is configured to rotatably support the holder by the main body portion and the cover, by bending an end portion of the float arm at a substantially right angle to make an end portion side of the float arm be a first end portion and, make a central side of the float arm before the first end portion be a second end portion, providing, in the holder, a first arm mounting portion configured to fix the first end portion, and a second arm mounting portion configured to fix the second end portion, providing, in the main body portion, a stopper configured to regulate a range of rotation of the holder, providing, in the holder, a first stopper configured to abut the stopper, and providing the first arm mounting portion and the first stopper on a straight hypothetical line extending through an axis of rotation of the holder, said hypothetical line being perpendicular to the axis of rotation the first stopper and the first arm mounting portion being placed on opposite sides on said hypothetical line with respect to the axis of rotation, wherein: the first arm mounting portion comprises a through hole configured to fix the first end portion, the second arm mounting portion comprises an opening configured to fix the second end portion, the second arm mounting portion is provided between the first arm mounting portion and the first stopper on an outer peripheral surface of the holder, and the angle of the first arm mounting portion and the second arm mounting portion about an axis of rotation of the holder is set to be a substantially right angle, and the angle of the second arm mounting portion and the first stopper about an axis of rotation of the holder is set to be a substantially right angle. a float arm including a float at one end portion thereof; a holder configured to hold the float arm and including a first rotating portion (2b2) and a second rotating portion (2b3); a main body portion including a first rotation support portion configured to rotatably support the first rotating portion (2b2); a cover including a second rotation support portion configured to rotatably support the second rotating portion (2b3); and a detecting portion, wherein, the liquid level detection device is configured to rotatably support the holder by the main body portion and the cover, by bending an end portion of the float arm at a substantially right angle to make an end portion side of the float arm be a first end portion and, make a central side of the float arm before the first end portion be a second end portion, providing, in the holder, a first arm mounting portion configured to fix the first end portion, and a second arm mounting portion configured to fix the second end portion, providing, in the main body portion, a stopper configured to regulate a range of rotation of the holder, providing, in the holder, a first stopper configured to abut the stopper, and providing the first arm mounting portion and the first stopper on a straight hypothetical line extending through an axis of rotation of the holder, said hypothetical line being perpendicular to the axis of rotation the first stopper and the first arm mounting portion being placed on opposite sides on said hypothetical line with respect to the axis of rotation, wherein: the first arm mounting portion comprises a through hole configured to fix the first end portion, the second arm mounting portion comprises an opening configured to fix the second end portion, the second arm mounting portion is provided between the first arm mounting portion and the first stopper on an outer peripheral surface of the holder, and the angle of the first arm mounting portion and the second arm mounting portion about an axis of rotation of the holder is set to be a substantially right angle, and the angle of the second arm mounting portion and the first stopper about an axis of rotation of the holder is set to be a substantially right angle. the first arm mounting portion comprises a through hole configured to fix the first end portion, the second arm mounting portion comprises an opening configured to fix the second end portion, the second arm mounting portion is provided between the first arm mounting portion and the first stopper on an outer peripheral surface of the holder, and the angle of the first arm mounting portion and the second arm mounting portion about an axis of rotation of the holder is set to be a substantially right angle, and the angle of the second arm mounting portion and the first stopper about an axis of rotation of the holder is set to be a substantially right angle.