To provide a method and apparatus for detecting an object using a microwave, whereby the detecting malfunction due to the field direction change of the microwave during propagating in a waveguide is avoided and the need of troublesome adjustment works for installation is eliminated.

The object detecting method for detecting the position or existence of an object or the distance from the object, based on that the object blocks or reflects a transmitted wave comprises radiating a microwave having a unidirectional field from a microwave oscillator 101 as a transmitted wave and inputting a received wave to a microwave detector 202 to detect it, and the microwave from the microwave oscillator is radiated as a transmitted wave after passing through a filter 104 which is capable of regulating the field of the microwave in a desired direction and allows only coincident field components of the microwave to the regulated field direction to pass through.