To inexpensively provide an illegality preventing device for preventing the occurrence of the malfunction of an photoelectric type coin detecting device due to a transparent light beam from the outside, and to apply the illegality preventing device to an existing coin selector.

The coin selector detects the passage of a coin based on signals from photoelectric type sensors 122 and 124 each including a light projecting part and a light receiving part arranged so as to be opposite to each other across a coin rolling path. The illegality preventing device of the coin detecting device of the coin selector is provided with an illegality preventing body constituted of transmitting materials, wherein the illegality preventing body is positioned on a rolling path 114 between the light projecting parts and the light receiving parts, is moved from a clearance between light projecting parts 129 and 131 and light receiving parts 133 and 135 by the rolling of a coin on the rolling path so that the light projection from the light projecting parts can be interrupted by the coin, and is held between the projecting parts and the light receiving parts at movement other than the movement of the coin.

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