With the object of providing a battery mounting structure and working machine which can improve the degrees of freedom in layout of constituent components including a battery, without restrictions in the mounting direction of the battery, it is configured to include a placement member provided at an upper part of an electrical component, a battery which is provided detachably to the placement member and drives the electrical component, and a connection member which extends from the electrical component towards the battery and can electrically connect the electrical component and the battery.