An imaging device comprising: a solid-state image-capture element comprising first lines (L1, L3, L5), on which first phase difference detection pixels, each of which receiving one of a pair of light bundles passing through aperture areas of an imaging optical system located at different positions, are arranged in a phase difference detection direction and second lines (L2, L4, L6) on which second phase difference detection pixels are arranged in the phase difference detection direction, each of which receiving the other of the pair of light bundles; an image-capture element driving unit configured to read out a signal from the solid-state image-capture element by a rolling shutter method; a phase difference information calculation unit configured to calculate phase difference information; and a focusing control unit configured to control a focus of the imaging optical system on the basis of the phase difference information calculated by the phase difference information calculation unit; characterized in that the solid-state image-capture element comprises a phase difference detection area in which two first lines and one second line are arranged, and one of the two first lines, the second line, and the other of the two first lines are arranged in this order in a direction orthogonal to the phase difference detection direction; wherein the phase difference information calculation unit is configured to calculate a first phase difference amount between a first signal group, which is read out from the first phase difference detection pixels of a first line, and a second signal group, which is read out from the second phase difference detection pixels of a second line adjacent to the first line from which signals are read out later than the first line, a second phase difference amount between the second signal group and a third signal group, which is read out from the first phase difference detection pixels of a further first line, wherein there is a predetermined number of lines between the second line and the further first line such that signals are read out from the further first line later than the second line, the second phase difference being calculated by using the first signal group, the second signal group and the third signal group, and to calculate a phase difference information by a calculation using the first phase difference amount and the second phase difference amount. a solid-state image-capture element comprising first lines (L1, L3, L5), on which first phase difference detection pixels, each of which receiving one of a pair of light bundles passing through aperture areas of an imaging optical system located at different positions, are arranged in a phase difference detection direction and second lines (L2, L4, L6) on which second phase difference detection pixels are arranged in the phase difference detection direction, each of which receiving the other of the pair of light bundles; an image-capture element driving unit configured to read out a signal from the solid-state image-capture element by a rolling shutter method; a phase difference information calculation unit configured to calculate phase difference information; and a focusing control unit configured to control a focus of the imaging optical system on the basis of the phase difference information calculated by the phase difference information calculation unit; the solid-state image-capture element comprises a phase difference detection area in which two first lines and one second line are arranged, and one of the two first lines, the second line, and the other of the two first lines are arranged in this order in a direction orthogonal to the phase difference detection direction; wherein the phase difference information calculation unit is configured to calculate a first phase difference amount between a first signal group, which is read out from the first phase difference detection pixels of a first line, and a second signal group, which is read out from the second phase difference detection pixels of a second line adjacent to the first line from which signals are read out later than the first line, a second phase difference amount between the second signal group and a third signal group, which is read out from the first phase difference detection pixels of a further first line, wherein there is a predetermined number of lines between the second line and the further first line such that signals are read out from the further first line later than the second line, the second phase difference being calculated by using the first signal group, the second signal group and the third signal group, and to a first phase difference amount between a first signal group, which is read out from the first phase difference detection pixels of a first line, and a second signal group, which is read out from the second phase difference detection pixels of a second line adjacent to the first line from which signals are read out later than the first line, a second phase difference amount between the second signal group and a third signal group, which is read out from the first phase difference detection pixels of a further first line, wherein there is a predetermined number of lines between the second line and the further first line such that signals are read out from the further first line later than the second line, the second phase difference being calculated by using the first signal group, the second signal group and the third signal group, and to