As the key component in on-chip mode-division multiplexing systems, a compact silicon photonic-lantern mode (de)multiplexer is proposed and demonstrated using the shallow-etched tilt slot waveguide. The proposed six-mode (de)multiplexer is designed as a constant coupling length of 11.7 µm for each mode conversion and eliminates the adiabatic transition tapers for cascaded asymmetric directional couplers, which have an ultra-short total length of 69 µm. The measured peak insertion losses of the fabricated device for all mode channels are less than 1.2 dB, and the crosstalk is below -12.6 dB in a 60 nm waveband. Additionally, the simulation results indicate that the device has a good fabrication tolerance. The proposed mode (de)multiplexer is scalable and could provide a feasible solution for the dense integration of on-chip mode division multiplexing systems.