1. An ultrasonic observation apparatus that transmits an ultrasonic wave to a specimen and receives the ultrasonic wave reflected from the specimen, the ultrasonic observation apparatus comprising: a computer configured to implement: a region of interest setting unit configured to set information on a position, and a length in a depth direction, of a region of interest in the specimen; a focus point calculation unit configured to: divide the region of interest into a plurality of partial regions of interest according to a number of focus points in the region of interest, wherein the number of focus points is a parameter associated with the length of the region of interest set by the region of interest setting unit; set one or more of the number of focus points in each of the plurality of partial regions of interest; and determine a transmission timing according to the one or more of the number of focus points set in each of the plurality of partial regions of interest; a transmitting and receiving unit configured to: perform transmission of a number of ultrasonic waves along a sound ray in the region of interest, wherein the number of ultrasonic waves correspond to the number of focus points, and wherein the transmitted ultrasonic waves are focused on the corresponding focus point set by the focus point calculation unit; and receive a number of ultrasonic waves reflected from the region of interest, wherein the ultrasonic waves received from the region of interest correspond to the focus points; a frequency analysis unit configured to calculate frequency spectra by analyzing the ultrasonic waves received by the transmitting and receiving unit with reference to the focus points; a feature data extracting unit configured to extract feature data of the frequency spectra calculated by the frequency analysis unit by approximating the frequency spectra; and an image processing unit configured to generate display image data based on the feature data extracted by the feature data extracting unit, wherein the focus point calculation unit is configured to: set the one or more of the focus points for a B-mode image for displaying brightness converted from amplitude of the ultrasonic wave reflected from the specimen, and use the one or more of the focus points for the B-mode image in the partial regions of interest, and wherein the feature data extracting unit comprises: an approximation unit configured to: approximate the frequency spectra with a linear equation by regression analysis; and calculate, as pre-correction feature data for characterizing the linear equation: a gradient and an intercept of the linear equation, and intensity at a particular frequency within a frequency band in the frequency spectra; and an attenuation correction unit configured to perform an attenuation correction process on the pre-correction feature data to extract the feature data of the frequency spectra, wherein the frequency analysis unit is configured to calculate the frequency spectra by acquiring a data group forming a part of a data array of the ultrasonic wave received by the transmitting and receiving unit and by performing fast Fourier transform on the data group, and wherein the frequency analysis unit is configured to acquire a multiple data groups for the sound ray, and is configured to calculate the frequency spectra using a data group of the multiple data groups which is closest to the one or more of the focus points.