A camera body includes a camera body connector and a recess to which an imaging unit including an optical system, an image pickup device, and an imaging unit connector is detachably attached to be placed therein. The recess includes a back wall, an upper wall, and a side wall to be opened to a lower side, a front side, and a lateral side of the camera body. The camera body has a guide mechanism to control a position of the camera body connector in relation to a position of the imaging unit connector. The imaging unit has a rear surface on which at least two guiding grooves provided to be extended between opposite edges of the imaging unit and an engagement plate section are formed. The imaging unit has a biasing member to bias the imaging unit toward the back wall. The guide mechanism has at least two guide protrusions provided on the back wall and inserted into the at least two guiding grooves and an engagement claw formed on the back wall so as to face the engagement plate section and to engage with the biasing member when the imaging unit is attached to the camera body.