Provided is an attachment structure for a water heater capable of easily and securely attaching the water heater to a wall surface without performing strict alignment, and capable of fine adjustment of an attachment position of the water heater even after the attachment. The attachment structure for the water heater includes a first metal fitting (1) having a wall surface attachment portion (11) configured to be attached to a wall surface (W), and a second metal fitting (2) having an instrument attachment portion (23) configured to be attached to a back surface of the instrument body (3). In the wall surface attachment portion 11, a support portion (12) configured to hang and support a weight of the water heater is extended in a direction separate from the wall surface (W). In the instrument attachment portion (23), an engagement portion configured to engage with the support portion (12) from above is extended in a direction separate from the instrument body (3), and a lateral length of the support portion (12) is set to enough length to slide the engagement portion in a horizontal direction.