An intake parameter estimating device is provided for estimating a tuning frequency of an internal combustion engine, which in turn can be used to estimate an intake air pressure of the internal combustion engine. The intake parameter estimating device basically has a fundamental frequency calculating section, an engine rotational speed detecting section and a tuning frequency calculating section. The fundamental frequency calculating section calculates a fundamental frequency of a pressure wave inside an air intake pipe based on a shape of the air intake pipe and speed of sound. The engine rotational speed detecting section detects an engine rotational speed. The tuning frequency calculating section calculates a tuning frequency of the pressure wave inside the air intake pipe based on the fundamental frequency and the engine rotational speed. The tuning frequency can then be used to estimate the intake air pressure of the internal combustion engine.