We investigated the behavior of a mixed-gas plasma flow driven by a compact plasma focus device into a perpendicular magnetic field, by using a one-dimensional hybrid particle-in-cell simulation. When the plasma flowed into the perpendicular magnetic field, some accelerated ions were generated in front of the plasma flow owing to the compression of the magnetic field. The behavior of the compressed magnetic field changed by mixing heavy ions with the collisionless plasma. The maximum velocity of the accelerated light ions was proportional to the square root of the average ion mass of the plasma. These results indicate that the effect of the multi-ion species strongly affects the injection of light ions.