To remotely detect an alcohol component in the compartment of a running vehicle in the running state of the vehicle.

A pulse-like laser beam LB1 with an alcohol absorbing wavelength λ1 is emitted to a running vehicle from a laser diode 1 and a pulse-like laser beam LB2 with a reference wavelength λ2 is emitted from a laser diode 2 so as to leave a time lag and both laser beams LB1, LB2 are detected by a common photodiode 3. A microprocessor 12 judges that an alcohol component is present in a compartment when alcohol concn. data Da calculated by subtracting light requirement data D1 with the alcohol absorbing wavelength λ1 from light requirement data D2 with the reference wavelength λ2 is a predetermined threshold Dref or more to output an alcohol detection signal Sa.