A dynamic mode AFM apparatus comprising: (a) a scanner [3; 103] for performing three-dimensional relative scanning of a cantilever [2; 102] and a sample [1; 101]; (b) a means for generating an AC signal of a resonance frequency in a mode with flexural vibration of the cantilever [2; 102]; (c) a means [9; 106] for exciting the flexural vibration of the cantilever [2; 102] with the resonance frequency in response to the signal from said means for generating said AC signal of said resonance frequency; (d) a means [10; 111] for generating an AC signal of a second frequency which is lower than the frequency of the flexural vibration; (e) a means [11; 112], connected to the means [10; 111] for generating said AC signal of said second frequency, for modulating a probe [2A; 102A]-sample [1; 101] distance of the cantilever [2; 102] with the second frequency; (f) a means [4; 104] for detecting vibration of the cantilever[2; 102]; (g) a means for detecting fluctuation of the resonance frequency from the detected vibration of the cantilever [2; 102]; characterized in that the apparatus further comprises: (h) a means for detecting a fluctuation component which is contained in a detected signal by the means for detecting the resonance frequency fluctuation and synchronized with a modulation signal of the probe [2A; 102A]- sample [1; 101] distance wherein an output signal from said means [10;111] for generating said AC signal of said second frequency is input into said means for detecting said fluctuation component; and (i) wherein an inclination signal of the resonance frequency against the probe [2A; 102A]-sample [1;101] distance is obtained from strength and polarity of the fluctuation component with said means for detecting said fluctuation component. (a) a scanner [3; 103] for performing three-dimensional relative scanning of a cantilever [2; 102] and a sample [1; 101]; (b) a means for generating an AC signal of a resonance frequency in a mode with flexural vibration of the cantilever [2; 102]; (c) a means [9; 106] for exciting the flexural vibration of the cantilever [2; 102] with the resonance frequency in response to the signal from said means for generating said AC signal of said resonance frequency; (d) a means [10; 111] for generating an AC signal of a second frequency which is lower than the frequency of the flexural vibration; (e) a means [11; 112], connected to the means [10; 111] for generating said AC signal of said second frequency, for modulating a probe [2A; 102A]-sample [1; 101] distance of the cantilever [2; 102] with the second frequency; (f) a means [4; 104] for detecting vibration of the cantilever[2; 102]; (g) a means for detecting fluctuation of the resonance frequency from the detected vibration of the cantilever [2; 102]; (h) a means for detecting a fluctuation component which is contained in a detected signal by the means for detecting the resonance frequency fluctuation and synchronized with a modulation signal of the probe [2A; 102A]- sample [1; 101] distance wherein an output signal from said means [10;111] for generating said AC signal of said second frequency is input into said means for detecting said fluctuation component; and (i) wherein an inclination signal of the resonance frequency against the probe [2A; 102A]-sample [1;101] distance is obtained from strength and polarity of the fluctuation component with said means for detecting said fluctuation component.