An image forming apparatus according to the present invention includes: a first sensor that is provided in a conveying path for a sheet and detects a first passage time of the sheet; a second sensor that is provided in a position different from a position of the first sensor in both a conveying direction of the sheet and a direction orthogonal to the conveying direction, and detects a second passage time of the sheet; a skew determining unit that calculates a skew amount of the sheet from a difference between the first passage time detected by the first sensor and the second passage time detected by the second sensor and determines occurrence of skew of the sheet on the basis of the skew amount; and a cause estimating unit that estimates, when the skew determining unit determines that the skew occurs, a cause of the occurrence of the skew.