Low-density choked flow through a parallel plate channel with a narrow gap is studied experimentally for a wide range of Reynolds numbers. In the region from continuum flow to slip flow, the choked flow is analyzed by one-dimensional flow approximation based on the integrated boundary layer equations, taking into account the slip at the channel walls. The calculated discharge coefficients and pressure distributions agree well with the experimental results for a wide range of Reynolds numbers, including the slip flow region. A nondimensional correlation equation of the discharge coefficient is proposed as a function of Reh_s/l for Reh_s/l<2×10². In the region from slip flow to molecular flow, the experimental results agree well with those of previous work. A nondimensional correlation equation of C_dl/h_s is proposed as a function of Re for 7<Re<5×10¹.