A semiconductor integrated circuit comprising: a cell layout region including circuit cells subject to power control, the supply and interruption of power to which is controlled by a power switch, and a main line pair laid out in the cell layout region, the main line pair comprising a first line and a second line, one of the first and second lines being a source voltage line and the other of the first and second lines being a reference voltage line; always-on circuit cells (50; 50A) which are connected to said first and second lines of the main line pair without said power switch connected therebetween, said always-on circuit cells being configured to be always powered after activation of said main line pair; and first and second branch lines (72,71) which branch from the main line pair in the cell layout region; wherein the circuit cells subject to power control are connected to the first line of the main line pair via the power switch and first branch line, and wherein the always-on circuit cells include a plurality of always-on circuit cells corresponding to branch connection circuit cells, said branch connection circuit cells being connected to the first line of the main line pair via the second branch line, and at least one always-on circuit cell corresponding to an individual connection circuit cell, said individual connection circuit cell being connected to the first line of the main line pair via an individual connection line without the second branch line and being connected to the second line of the main line pair via a further branch line (61/62) that is also connected to circuit cells subject to power control. a cell layout region including circuit cells subject to power control, the supply and interruption of power to which is controlled by a power switch, and a main line pair laid out in the cell layout region, the main line pair comprising a first line and a second line, one of the first and second lines being a source voltage line and the other of the first and second lines being a reference voltage line; circuit cells subject to power control, the supply and interruption of power to which is controlled by a power switch, and a main line pair laid out in the cell layout region, the main line pair comprising a first line and a second line, one of the first and second lines being a source voltage line and the other of the first and second lines being a reference voltage line; always-on circuit cells (50; 50A) which are connected to said first and second lines of the main line pair without said power switch connected therebetween, said always-on circuit cells being configured to be always powered after activation of said main line pair; and first and second branch lines (72,71) which branch from the main line pair in the cell layout region; wherein the circuit cells subject to power control are connected to the first line of the main line pair via the power switch and first branch line, and wherein the always-on circuit cells include a plurality of always-on circuit cells corresponding to branch connection circuit cells, said branch connection circuit cells being connected to the first line of the main line pair via the second branch line, and at least one always-on circuit cell corresponding to an individual connection circuit cell, said individual connection circuit cell being connected to the first line of the main line pair via an individual connection line without the second branch line and being connected to the second line of the main line pair via a further branch line (61/62) that is also connected to circuit cells subject to power control. the circuit cells subject to power control are connected to the first line of the main line pair via the power switch and first branch line, and wherein the always-on circuit cells include a plurality of always-on circuit cells corresponding to branch connection circuit cells, said branch connection circuit cells being connected to the first line of the main line pair via the second branch line, and at least one always-on circuit cell corresponding to an individual connection circuit cell, said individual connection circuit cell being connected to the first line of the main line pair via an individual connection line without the second branch line and being connected to the second line of the main line pair via a further branch line (61/62) that is also connected to circuit cells subject to power control.