Recently, interest in automatic crack detection on concrete structure images for non-destructive inspection has been increasing. In general, there are various noises such as irregularly illuminated conditions, shading, blemishes and divots in the concrete images. These lead to difficulties for automatic crack detection. This paper presents two pre-processings in order to remove such noises for crack detection. First, slight variations like irregularly illuminated conditions and shading are removed from concrete images by the subtraction pre-processing with the smoothed image. Secondly, a line filter based on the Hessian matrix is used to emphasize line structures associated with cracks. Finally, thresholding processing is used to separate cracks from background. The performance of the proposed method is evaluated by ROC analysis with 50 real images. The experimental results show that the proposed method is effective for detecting cracks on noisy concrete images.