Provided is a liquid level detection device which is configured so that an arm can be easily mounted to a holder after the holder is pivotably mounted using a cover and a main body portion. An end of a float arm is bent at a substantially right angle, and the end side of the float arm is defined as a first end portion. The portion of the float arm which is located closer to the center of the float arm than the first end portion is defined as a second end portion. A first arm mounting portion to which the first end portion is affixed and second arm mounting portions to which the second end portion is affixed are provided to a holder. A stopper for restricting the pivot range of the holder is provided to a main body portion. A first stopper which comes into contact with the stopper is provided to the holder. The first arm mounting portion and the first stopper are provided on a line passing through the pivot axis of the holder and perpendicular to the pivot axis.