To shorten a train time interval at low costs by detecting the position of a train based on a signal from the light receiver of a light projection and receiving means disposed to shut off a light by the train and sending it out to a succeeding train.

Projectors D1 to Dn and light receivers R1 to Rn are disposed by keeping specified intervals and sandwiching a rail (r). The projectors and receivers D1 to Dn and R1 to Rn are set in a position for shutting off a light from an optical axis when trains (a) and (b) are traveled on the rail (r). A controller 4 analyzes the signals of the receivers R1, R2... received by the receiver 3 and produces information regarding the positions of the trains (a) and (b). The positional information is then outputted to a transmitter 5. The transmitter 5 sends the positional information for the trains (a) and (b) via a connecting transformer (t) and a signal line L to the trains (a) and (b). Thus, the time interval between the trains is shortened at low costs.