To provide a float type liquid level detector capable of fixing firmly a stopper for regulating vertical motion of a float going up and down in response to a liquid level height, without damaging a stem.

The stopper 5 for regulating vertical motion of the float 3 has a pair of fastening seats 6a, 6b projected sideways from both ends of a segmental part of a C-shaped ring engaged with an outer circumference of the stem 1, a tapped hole 7a for bolt screw insertion is engraved in the one fastening seat 6a, a through hole 7b for bolt insertion is drilled in the other fastening seat 6b, an outer face of the fastening seat 6b is formed into an up-grade sloped face 8 ranging over from a root part toward a tip part direction, and an inner circumference of the C-shaped ring is brought into pressure contact with the outer circumference of the stem 1 to be fixed, by inserting the fastening bolt 9 from the bolt insertion through hole 7b to be screw-inserted into the bolt screw-insertion tapped hole 7a.