A projection system comprising: an imaging unit that captures a subject to generate a first captured image; a projection unit projects a projection image (G3, G320) corresponding to the first captured image onto the subject; a display unit that displays an image, an operation unit that inputs a user operation, and a controller having a first operation mode and a second operation mode, the first operation mode being a mode to generate the projection image (G3, G320) corresponding to the first captured image and to cause the projection unit to project the projection image (G3, G320), and the second operation mode being a mode to adjust a positional relationship that brings a position in the first captured image and a position in the projection image (G3, G320) into correspondence with each other, characterized in that in the second operation mode, the controller causes the projection unit to project a marker image (G1, G1a, G2) including a marker (P0, P1, P2, P3, P4, P20) indicating a reference in the positional relationship, acquires a second captured image generated by the imaging unit capturing an image of the projected marker image (G1, G1a, G2), and adjusts the positional relationship, based on the marker (P0, P1, P2, P3, P4, P20) in the marker image (G1, G1a, G2) and the marker in the second captured image in the first operation mode, referring to the positional relationship adjusted in the second operation mode, the controller generates the projection image (G3, G320) where the position in the first captured image and the position in the projection image (G3, G320) are in correspondence with each other, in the second operation mode, the controller controls and causes the display unit to display the marker (P0, P1, P2, P3, P4, P20) in the marker image (G1, G1a, G2), in a superimposed manner, on the second captured image, and in the second operation mode, the controller adjusts the positiona relationship according to the user operation that is input from the operation unit. an imaging unit that captures a subject to generate a first captured image; a projection unit projects a projection image (G3, G320) corresponding to the first captured image onto the subject; a display unit that displays an image, an operation unit that inputs a user operation, and a controller having a first operation mode and a second operation mode, the first operation mode being a mode to generate the projection image (G3, G320) corresponding to the first captured image and to cause the projection unit to project the projection image (G3, G320), and the second operation mode being a mode to adjust a positional relationship that brings a position in the first captured image and a position in the projection image (G3, G320) into correspondence with each other, characterized in that in the second operation mode, the controller causes the projection unit to project a marker image (G1, G1a, G2) including a marker (P0, P1, P2, P3, P4, P20) indicating a reference in the positional relationship, acquires a second captured image generated by the imaging unit capturing an image of the projected marker image (G1, G1a, G2), and adjusts the positional relationship, based on the marker (P0, P1, P2, P3, P4, P20) in the marker image (G1, G1a, G2) and the marker in the second captured image in the first operation mode, referring to the positional relationship adjusted in the second operation mode, the controller generates the projection image (G3, G320) where the position in the first captured image and the position in the projection image (G3, G320) are in correspondence with each other, in the second operation mode, the controller controls and causes the display unit to display the marker (P0, P1, P2, P3, P4, P20) in the marker image (G1, G1a, G2), in a superimposed manner, on the second captured image, and in the second operation mode, the controller adjusts the positiona relationship according to the user operation that is input from the operation unit. in the second operation mode, the controller causes the projection unit to project a marker image (G1, G1a, G2) including a marker (P0, P1, P2, P3, P4, P20) indicating a reference in the positional relationship, acquires a second captured image generated by the imaging unit capturing an image of the projected marker image (G1, G1a, G2), and adjusts the positional relationship, based on the marker (P0, P1, P2, P3, P4, P20) in the marker image (G1, G1a, G2) and the marker in the second captured image in the first operation mode, referring to the positional relationship adjusted in the second operation mode, the controller generates the projection image (G3, G320) where the position in the first captured image and the position in the projection image (G3, G320) are in correspondence with each other, in the second operation mode, the controller controls and causes the display unit to display the marker (P0, P1, P2, P3, P4, P20) in the marker image (G1, G1a, G2), in a superimposed manner, on the second captured image, and in the second operation mode, the controller adjusts the positiona relationship according to the user operation that is input from the operation unit.