To provide an adapter for a sensor for simply and rapidly performing sensor replacement.

This adapter 4 for a sensor is equipped with a body 5, a positioning projection 5d, a fixation means V, and a position adjustment means W. The body 5 has an insertion hole 5a for inserting a proximity sensor 3 therein. The positioning projection 5d is formed so as to inwardly protrude from an end part of the insertion hole 5a for positioning the sensor 3 at a definite position in the hole 5a. The fixation means V has a slit 5b extended axially of the hole 5a for removably fixing the sensor 3 in the hole 5a and a bolt 6 for narrowing the slit 5b. The adjustment means W comprises a male screw part 5j formed on the periphery of the body 5 for position-adjusting and fixing the body 5 to a bracket 2, and nuts 7 and 7 threadedly engaging with the screw part 5j.