To provide a railroad model device which activates various kinds of devices, such as railroad crossings, block signals or points, without malfunctions by installing sensor devices inconspicuously alongside tracks and automatically and surely detecting the model vehicles traveling on the tracks.

This railroad model device comprises ballast beds 11 to which the tracks are mounted, supporting members 13 (21) which are erected in the side parts of the ballast beds 11 and the sensor devices 14 (22) which are mounted and supported at these supporting members 13 (21). Light emitting and receiving parts which are the sensor parts of these sensor devices 14 (22) radiate detecting media from above to below the tracks 12 so as to detect the passage of the model vehicles traveling on the tracks 12 laid on the ballast beds 11.