To provide a device for detecting the passage of an object, capable of inexpensively realizing the detection of the passage of the object with high reliability.

In an adjustment method of a light reflection sensor in a device for detecting the passage of an object to be detected such as coin by using the light reflection sensor, a first detection output level V1 of a light receiving amount by a light receiving element in a state that the object to be detected is detected, and a second detection output level V2 of a light receiving amount by the light receiving element in a state that the object to be detected is not detected, are measured while varying a light emitting amount from a light emitting element of the optical sensor, to determine the difference V1-V2 between the first detection output level and the second detection output level, and the light emitting amount of the maximum difference V1-V2 is used as an adjustment value.