Radial velocity variation induced by stellar activity (also known as "RV jitter") is one of the biggest issues in the search for low-mass planets and measurements of their masses by the RV method. RV jitter is known to have multiple causes, including spots or plages, magnetic effects, and convective (blue-)shifts on the stellar surface. A large number of studies in the past investigated RV jitter, attempting to clarify their behavior and correlation with light curves and spectroscopic activity indicators, but those studies were mostly based on numerically simulated line-profile variations, in which the modeling of jitters was computationally expensive and their behavior was often non-intuitive. In this poster, we introduce a new analytic description of RV jitters using a simple, but physically-motivated toy model. The analytic calculation takes into account multiple components causing line-profile variations, providing a more quantitative and intuitive understanding of the behaviors of RV jitter. Comparing the analytic equations with RV measurements for young stars obtained by IRD on the Subaru telescope, we show that the larger amplitude of RV jitters at longer wavelengths for active M dwarfs can be naturally explained by the relative variation in the depth of of molecular lines. We also discuss the implications of the analytic description of RV jitter for various types of stars.